From abc40d69d5232cf294906b34713af2343492a694 Mon Sep 17 00:00:00 2001
From: Romain Vuillemot <romain.vuillemot@gmail.com>
Date: Wed, 23 Oct 2024 18:13:18 +0200
Subject: [PATCH] Solution lab 2
---
labs-solutions/02-recursion-exercises.ipynb | 1325 +++++++++++++++++++
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create mode 100644 labs-solutions/02-recursion-exercises.ipynb
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@@ -0,0 +1,1325 @@
+{
+ "cells": [
+ {
+ "cell_type": "markdown",
+ "id": "a4e4fad3",
+ "metadata": {
+ "slideshow": {
+ "slide_type": "slide"
+ }
+ },
+ "source": [
+ "# UE5 Fundamentals of Algorithms\n",
+ "# Lab 2: Recursion"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "a8adef9b",
+ "metadata": {
+ "slideshow": {
+ "slide_type": "skip"
+ }
+ },
+ "source": [
+ "---"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "eee7125e-cd0b-4aff-ac6d-fba530b13050",
+ "metadata": {
+ "tags": []
+ },
+ "source": [
+ "For each of the following questions:\n",
+ "- In the `# YOUR CODE HERE` cell, remove `raise NotImplementedError()` to write your code\n",
+ "- Write an example of use of your code or make sure the given examples and tests pass\n",
+ "- Add extra tests in the `#Tests` cell\n",
+ "\n",
+ "Recall on recursion:\n",
+ "\n",
+ "- Find a base case to stop the recursion\n",
+ "- Fin a decomposition of the problem to reach it\n",
+ "- Don't reach the Python recursion limits or infinite loops\n",
+ "\n",
+ "To compare iterative and recursive functions you may use the following time comparison functions:"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 11,
+ "id": "f6c23281-9c3d-488a-acb9-069964faff4b",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "Elapsed time: 1.0082 seconds\n"
+ ]
+ }
+ ],
+ "source": [
+ "import time\n",
+ "t1 = time.time()\n",
+ "# YOUR CODE\n",
+ "time.sleep(1)\n",
+ "dt = time.time() - t1\n",
+ "print(f\"Elapsed time: {dt:.4f} seconds\")"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "568202fd",
+ "metadata": {
+ "slideshow": {
+ "slide_type": "subslide"
+ }
+ },
+ "source": [
+ "### Example: Find the maximum value in a list (iterative)\n",
+ "\n",
+ "Write a function `find_maximum_iterative` that takes a list of numbers as input and returns the maximum value in the list. For this question, you are not allowed to use built-in functions like `max()`."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 16,
+ "id": "431fe8c1-91d1-40f3-a7a4-f4a3770a4a01",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def find_maximum_iterative(L): \n",
+ " if len(L) == 0:\n",
+ " raise ValueError(\"the list is empty\")\n",
+ "\n",
+ " max_val = L[0]\n",
+ " for num in L:\n",
+ " if num > max_val:\n",
+ " max_val = num\n",
+ " return max_val"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 17,
+ "id": "f6baae3c-3660-4add-ab4b-48016cba3030",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "9"
+ ]
+ },
+ "execution_count": 17,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "find_maximum_iterative([1, 3, 5, 7, 9]) # 9"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 18,
+ "id": "e68b3e9a-418f-4950-9f27-18bb0fe90794",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_find_maximum_iterative",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert find_maximum_iterative([1, 3, 5, 7, 9]) == 9\n",
+ "assert find_maximum_iterative([-1, -5, -3]) == -1\n",
+ "assert find_maximum_iterative([42]) == 42\n",
+ "assert find_maximum_iterative([4, 8, 8, 2, 7]) == 8\n",
+ "assert find_maximum_iterative([-10, -5, -8, -2, -7]) == -2"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "772184f4-6af4-4996-9bb1-da46c31891f8",
+ "metadata": {},
+ "source": [
+ "To test exceptions you can use the following code:"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 19,
+ "id": "a4201264-48f2-44f3-817b-a008500aed0c",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "try:\n",
+ " find_maximum_iterative([])\n",
+ "except ValueError:\n",
+ " assert True"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "612dc873-419b-42c5-be36-0accd03ffa79",
+ "metadata": {},
+ "source": [
+ "### Exercise 1: Find the maximum value in a list (recursive)\n",
+ "\n",
+ "Write a recursive version to find the max value in a list of integers. You may use the `max()` function for the recursive call but not as a unique solution. Compare with the iterative version from the example."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 22,
+ "id": "07668fd8",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "find_maximum_recursive",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def find_maximum_recursive(L):\n",
+ " ### BEGIN SOLUTION\n",
+ " if len(L) == 1:\n",
+ " return L[0]\n",
+ " else:\n",
+ " return max(L[0], find_maximum_recursive(L[1:]))\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 31,
+ "id": "f9784710-4b2b-434c-bc47-da46fa410749",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "9"
+ ]
+ },
+ "execution_count": 31,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "find_maximum_recursive([1, 3, 5, 7, 9]) # 9"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 32,
+ "id": "9b0161f8-0539-4e5e-921c-1886e61c0783",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_find_maximum_recursive",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert find_maximum_iterative([-10, -5, -8, -2, -7]) == find_maximum_recursive([-10, -5, -8, -2, -7])"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "25ba2ca3-b4f6-4f1a-8b95-b3e1394ee834",
+ "metadata": {},
+ "source": [
+ "Hints: find don't use `for` or `sort`."
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "005efd41-baa1-4505-b80e-3644d61ea094",
+ "metadata": {},
+ "source": [
+ "### Exercise 2: Sum of digits\n",
+ "\n",
+ "Write a recursive function that calculates the sum of the digits so that given a positive integer (e.g. `123` of type `int`), it return the sum of digits it contains (e.g. for `123` it returns `6`)."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 18,
+ "id": "de424156-0b9b-41d0-8e38-ce335f35cec0",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "sum_of_digits",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def sum_of_digits(n):\n",
+ " ### BEGIN SOLUTION\n",
+ " if n < 10:\n",
+ " return n\n",
+ " else:\n",
+ " return n % 10 + sum_of_digits(n // 10)\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 19,
+ "id": "cec0caca-cb2c-4e4d-b004-27b3cf2ff611",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "1"
+ ]
+ },
+ "execution_count": 19,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "sum_of_digits(10) # 1"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 20,
+ "id": "bf276ca2-48ed-4e87-80f2-776f54b7062b",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_sum_of_digits",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert sum_of_digits(10) == sum_of_digits(100000)\n",
+ "assert sum_of_digits(0) == 0\n",
+ "assert sum_of_digits(123) == 6\n",
+ "assert sum_of_digits(56) == 11"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "e2de630a-f9bd-4d45-959b-430e34cc9044",
+ "metadata": {
+ "tags": []
+ },
+ "source": [
+ "### Exercise 3: Calculate the n-th power value\n",
+ "\n",
+ "Calculate the n-th power of a number using a recursive function."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 39,
+ "id": "abca03a0-7bcd-4ee6-b109-ff2f2da52bb6",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "power",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def power(base, exponent):\n",
+ " ### BEGIN SOLUTION\n",
+ " if exponent == 0:\n",
+ " return 1\n",
+ " else:\n",
+ " return base * power(base, exponent - 1)\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 52,
+ "id": "abddd3b1-f75f-4cb6-a09e-54eed489c5b0",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "1024"
+ ]
+ },
+ "execution_count": 52,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "power(2, 10) # 1024"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 38,
+ "id": "8a6605fe-4f6f-45de-84a3-7601e2e2e6f6",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_power",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert power(2, 10) == 1024\n",
+ "assert power(2, 0) == 1\n",
+ "assert power(5, 3) == 125\n",
+ "assert power(1, 0) == 1 ** 0"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "715100d3-fc21-49b9-a66d-b5243b4a279d",
+ "metadata": {
+ "tags": []
+ },
+ "source": [
+ "### Exercise 4: Reverse a string\n",
+ "\n",
+ "Write a recursive function that takes a string s as input and returns the reversed version of the string."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 22,
+ "id": "ddc9826a-0863-4777-a08d-81b66652b5a5",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "reverse_string",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def reverse_string(s):\n",
+ " ### BEGIN SOLUTION\n",
+ " if len(s) == 0 or len(s) == 1:\n",
+ " return s\n",
+ " else:\n",
+ " return reverse_string(s[1:]) + s[0]\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 23,
+ "id": "13acad7e-d03c-4ea6-ad86-baf02e0910eb",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "'niamoR'"
+ ]
+ },
+ "execution_count": 23,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "reverse_string(\"Romain\") # niamoR"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 24,
+ "id": "453c8e04-6cd9-4581-a206-dd479b6115cd",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_reverse_string",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert reverse_string(\"\") == \"\"\n",
+ "assert reverse_string(\"AA\") == \"AA\"\n",
+ "assert reverse_string(\"ABC\") == \"CBA\""
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "c1587148-f816-4af2-8f3a-6d8a8480d54d",
+ "metadata": {
+ "tags": []
+ },
+ "source": [
+ "Write another version in an iterative way and compare with the recursive one."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 25,
+ "id": "159b6d78-03ae-4cf8-8545-e822b7160b32",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "cell-ead02fa889911e42",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def iterative_reverse_string(s):\n",
+ " ### BEGIN SOLUTION\n",
+ " reversed_str = \"\"\n",
+ " for char in s:\n",
+ " reversed_str = char + reversed_str\n",
+ " return reversed_str\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 26,
+ "id": "0dcdbd99-5f57-4d1c-bc31-8f8afc617d0e",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "'niamoR'"
+ ]
+ },
+ "execution_count": 26,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "iterative_reverse_string(\"Romain\")"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 48,
+ "id": "43e10b0c",
+ "metadata": {},
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert iterative_reverse_string(\"Romain\") == reverse_string(\"Romain\")"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "5ab8f3c9-ddee-45ab-a013-fdd67d9853e0",
+ "metadata": {},
+ "source": [
+ "### Exercise 5: Convert an interative suite into a recursive tail function\n",
+ "\n",
+ "Convert an iterative function into a recursive tail function (a function where the last operation is the recursive call)."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 54,
+ "id": "219add7f",
+ "metadata": {
+ "slideshow": {
+ "slide_type": "subslide"
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# iterative function\n",
+ "def sequence(n):\n",
+ " u = 1\n",
+ " while n > 0:\n",
+ " u = 2 * u + 1\n",
+ " n -= 1\n",
+ " return u"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 55,
+ "id": "0787df24-8234-4286-b910-5f9e456dd279",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "The result is 15\n"
+ ]
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "print(\"The result is {}\".format(sequence(3)))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 56,
+ "id": "9c17cf1b-6d05-4589-af2b-c05cfcc33202",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "sequence_recursive_tail",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def sequence_recursive_tail(n):\n",
+ " ### BEGIN SOLUTION\n",
+ " if n == 0:\n",
+ " return 1\n",
+ " return 2 * sequence_recursive_tail(n - 1) + 1\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 57,
+ "id": "43507c43-de61-414d-b389-c0a771ad9e0c",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "The result is still 15\n"
+ ]
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "print(\"The result is still {}\".format(sequence_recursive_tail(3)))"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 59,
+ "id": "dd923b7c-0cab-4678-8dc3-aad2ab9b25f9",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_sequence_recursive_non_tail",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "slideshow": {
+ "slide_type": "slide"
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert sequence_recursive_tail(3) == sequence(3) == 15"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "3c28b36a",
+ "metadata": {
+ "slideshow": {
+ "slide_type": "subslide"
+ }
+ },
+ "source": [
+ "### Exercise 6: Check if a word is a palindrom\n",
+ "\n",
+ "Write a function that takes a string as input and returns `True` if the word is a palindrome (i.e., it reads the same forwards and backwards), and `False` otherwise."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 2,
+ "id": "51bb3d08",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "annagram_rec",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def palindrom_rec(word):\n",
+ " ### BEGIN SOLUTION\n",
+ " if len(word) < 2: \n",
+ " return True\n",
+ " return (word[0] == word[-1]) and palindrom_rec(word[1:len(word)-1])\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 3,
+ "id": "0c279628-9b96-4687-8e20-a954ab646e0f",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "True"
+ ]
+ },
+ "execution_count": 3,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "palindrom_rec(\"laval\")"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 4,
+ "id": "cf6fa61a-7c6f-4a32-96c2-b9fd50deacc6",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_annagram_rec",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert palindrom_rec(\"\")\n",
+ "assert palindrom_rec(\"AA\")\n",
+ "assert not palindrom_rec(\"ABC\")\n",
+ "assert palindrom_rec(\"ABA\")\n",
+ "assert palindrom_rec(\"LAVAL\")\n",
+ "assert palindrom_rec(\"toto\") == False"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "798c2875-7940-488a-8458-ad08f6a71c70",
+ "metadata": {},
+ "source": [
+ "### Exercise 7: Calculate GCD\n",
+ "\n",
+ "Given two positive integers, write a recursive function to calculate their Greatest Common Divisor (GCD). The GCD of two integers is the largest integer that divides both numbers without leaving a remainder. Compare with the following iterative function:"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 66,
+ "id": "48c65c83-be0c-41c4-8c04-1d29ac4415cb",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def iterative_gcd(a, b):\n",
+ " while b:\n",
+ " a, b = b, a % b\n",
+ " return a"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 67,
+ "id": "bf6e1a76",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "recursive_gcd",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def recursive_gcd(a, b):\n",
+ " ### BEGIN SOLUTION\n",
+ " if b == 0:\n",
+ " return a\n",
+ " else:\n",
+ " return recursive_gcd(b, a % b)\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 68,
+ "id": "4f1feace",
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "2"
+ ]
+ },
+ "execution_count": 68,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "recursive_gcd(10, 2)"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 69,
+ "id": "e6ff1765-ff4b-49a5-80d3-684d2627e961",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_recursive_gcd",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert iterative_gcd(10, 2) == recursive_gcd(10, 2)"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "d8b05edf-9536-4fc1-bfcc-ddbbeee426fc",
+ "metadata": {},
+ "source": [
+ "### Exercise 8: Check if a list is sorted\n",
+ "\n",
+ "Write a recursive function that takes a list of numbers as input and returns `True` if the list is sorted in non-decreasing order and `False` otherwise."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 71,
+ "id": "1661dfb5-88f2-411f-8fe2-63bbaa29ce72",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "calculate_average_recursive",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def is_sorted(L):\n",
+ " ### BEGIN SOLUTION\n",
+ " if len(L) <= 1:\n",
+ " return True\n",
+ " else:\n",
+ " return L[0] <= L[1] and is_sorted(L[1:])\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 72,
+ "id": "0c5c72c6-3237-4f98-ab96-50a1838b833f",
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "True"
+ ]
+ },
+ "execution_count": 72,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "is_sorted([1, 2, 3, 4, 5])"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 73,
+ "id": "9f18b6b7-d980-4a72-a2a8-3aa201003d21",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_calculate_average_recursive",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert is_sorted([2, 3])\n",
+ "assert is_sorted([])\n",
+ "assert is_sorted([3, 2]) == False"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "79eef392-1d3d-46c0-aeee-ac805686e6f1",
+ "metadata": {},
+ "source": [
+ "### Exercise 9: Check for prime number\n",
+ "\n",
+ "Write a recursive function that checks if a given integer is a prime number. A prime number is a natural number greater than 1 that has no divisors other than 1 and itself."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 74,
+ "id": "ac374a08-11c9-47e6-ba11-419549911266",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "is_prime_recursive",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def is_prime_recursive(n, divisor=2):\n",
+ " ### BEGIN SOLUTION\n",
+ " if n < 2:\n",
+ " return False\n",
+ " \n",
+ " if n == 2:\n",
+ " return True\n",
+ " \n",
+ " if n % divisor == 0:\n",
+ " return False\n",
+ " \n",
+ " if divisor * divisor > n:\n",
+ " return True\n",
+ " \n",
+ " return is_prime_recursive(n, divisor + 1)\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 75,
+ "id": "996fc91f",
+ "metadata": {},
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "True"
+ ]
+ },
+ "execution_count": 75,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "is_prime_recursive(3)"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 66,
+ "id": "5be1051c-3b60-4810-b855-6f8575ad6380",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_is_prime_recursive",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert is_prime_recursive(3) "
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "5423682d-c31f-4a8d-9a0f-6812de7b1ae3",
+ "metadata": {},
+ "source": [
+ "### Exercise 10: Count occurrences of an element in a list"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 79,
+ "id": "cfeb0ad0-ed82-499e-9af3-64923291a0e7",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "count_occurrences",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def count_occurrences(L, target, index=0):\n",
+ " ### BEGIN SOLUTION\n",
+ " if index == len(L):\n",
+ " return 0\n",
+ " \n",
+ " count = (1 if L[index] == target else 0)\n",
+ " \n",
+ " return count + count_occurrences(L, target, index + 1)\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 81,
+ "id": "49daec07-00b3-412e-ad44-5bafadbd9f36",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "4"
+ ]
+ },
+ "execution_count": 81,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "count_occurrences([1, 2, 3, 4, 2, 2, 5, 6, 2], 2)"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 68,
+ "id": "14a2eb85-1126-4506-93bb-4bf624d046b6",
+ "metadata": {
+ "nbgrader": {
+ "grade": true,
+ "grade_id": "correct_count_occurrences",
+ "locked": true,
+ "points": 1,
+ "schema_version": 3,
+ "solution": false,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert count_occurrences([1, 2, 3, 4, 2, 2, 5, 6, 2], 2) == 4"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "88255769-ea62-4910-a459-109cb03e94d2",
+ "metadata": {},
+ "source": [
+ "## Bonus"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "e6bcb281-7f97-406a-ae20-729dddd518a3",
+ "metadata": {
+ "tags": []
+ },
+ "source": [
+ "### Exercise 11: 2D Binary search\n",
+ "\n",
+ "We want to search for a target value in a 2D matrix where:\n",
+ "\n",
+ "- Each row is sorted in ascending order.\n",
+ "- The first element of each row is greater than the last element of the previous row.\n",
+ "\n",
+ "Implement a recursive function to solve this problem (hint: use a similar approach to binary search in a 1D array)."
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 101,
+ "id": "e3e14407-2567-4531-bb8e-b35a6ba6d036",
+ "metadata": {
+ "nbgrader": {
+ "grade": false,
+ "grade_id": "cell-fba8f66061fb46f3",
+ "locked": false,
+ "schema_version": 3,
+ "solution": true,
+ "task": false
+ },
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "def binary_search_2D(matrix, target, left=0, right=None):\n",
+ " ### BEGIN SOLUTION\n",
+ " if right is None:\n",
+ " if not matrix or not matrix[0]:\n",
+ " return False\n",
+ " \n",
+ " rows = len(matrix)\n",
+ " cols = len(matrix[0])\n",
+ " right = rows * cols - 1\n",
+ "\n",
+ " if left > right: # base case\n",
+ " return False\n",
+ "\n",
+ " mid = (left + right) // 2\n",
+ " mid_value = matrix[mid // len(matrix[0])][mid % len(matrix[0])]\n",
+ "\n",
+ " if mid_value == target:\n",
+ " return True\n",
+ " elif mid_value < target:\n",
+ " return binary_search_2D(matrix, target, mid + 1, right) \n",
+ " else:\n",
+ " return binary_search_2D(matrix, target, left, mid - 1)\n",
+ " ### END SOLUTION"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 95,
+ "id": "291b699a-519c-41ba-9a7d-1cb055f78b40",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "m = [\n",
+ " [1, 3, 5, 7],\n",
+ " [10, 11, 16, 20],\n",
+ " [23, 30, 34, 50],\n",
+ " [60, 70, 80, 90]\n",
+ "]"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 98,
+ "id": "6c7215d2-f99a-41d1-a931-3623ab094674",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [
+ {
+ "data": {
+ "text/plain": [
+ "True"
+ ]
+ },
+ "execution_count": 98,
+ "metadata": {},
+ "output_type": "execute_result"
+ }
+ ],
+ "source": [
+ "# Example of use\n",
+ "binary_search_2D(m, 3) # True"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 100,
+ "id": "38f7f201-26d9-42c3-86dc-ef8712eb4167",
+ "metadata": {
+ "tags": []
+ },
+ "outputs": [],
+ "source": [
+ "# Tests\n",
+ "assert binary_search_2D(m, 11) == True\n",
+ "assert binary_search_2D(m, 15) == False"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "id": "d30f78d3-7916-4464-952d-8db56bc4cdb8",
+ "metadata": {
+ "tags": []
+ },
+ "source": [
+ "## Other exerices\n",
+ "\n",
+ "- Write a recursive version of the Ackerman function as defined [in this page](https://mathworld.wolfram.com/AckermannFunction.html) - [solution]( https://github.com/chkydebug/Ackerman-python/blob/main/Ackerman.py)\n",
+ "- Solve the [Tower of Hanoï problem](https://en.wikipedia.org/wiki/Tower_of_Hanoi) in a recursive way"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": null,
+ "id": "53fb4e2e-a123-4145-94d0-0323c886e1bd",
+ "metadata": {},
+ "outputs": [],
+ "source": []
+ }
+ ],
+ "metadata": {
+ "celltoolbar": "Slideshow",
+ "kernelspec": {
+ "display_name": "Python 3 (ipykernel)",
+ "language": "python",
+ "name": "python3"
+ },
+ "language_info": {
+ "codemirror_mode": {
+ "name": "ipython",
+ "version": 3
+ },
+ "file_extension": ".py",
+ "mimetype": "text/x-python",
+ "name": "python",
+ "nbconvert_exporter": "python",
+ "pygments_lexer": "ipython3",
+ "version": "3.10.9"
+ }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}
--
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