Adding 2nd assignment - recursion

Fundamental_Recursion/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 4.0)
+project(Fundamental_Recursion)
+
+set(CMAKE_CXX_STANDARD 20)
+
+add_executable(Fundamental_Recursion
+        main.cpp
+        utils.cpp
+        Utils.h
+)

Fundamental_Recursion/Utils.cpp

@@ -0,0 +1,132 @@
+#include <iostream>
+#include <random>
+#include <string>
+#include "Utils.h"
+
+void printNaturalNumber(const int n)
+{
+    if (n == 0)
+        return;
+    // "Digs down" until n = 0, then prints all natural numbers on the way back up
+    printNaturalNumber(n-1);
+    std::cout << n << " ";
+}
+
+int calculateFactorial(const int n)
+{
+    if (n <= 1)
+        return 1;
+     // "Digs down" until n <= 1, then multiplies by n for every step back up
+    return n * calculateFactorial(n-1);
+}
+
+int power(const int base,const int exp)
+{
+    if (exp == 0 || base == 1 || base == 0)
+        return 1;
+    // "Digs down" until exp <= 0, then multiplies base with the base for every step back up
+    return base * power(base, exp - 1);         // The simplest to write, not the most efficient - O(n)
+
+    // int half = power(base / 2, exp);
+    // if (exp % 2 == 0)
+    //     return half * half;
+    // else
+    //     return base * half * half;           // More efficient implementation, reduces the recursive call by half
+                                                // O(log n)
+
+}
+
+int fibonacci(const int n)
+{
+    if (n == 0)
+        return 0;
+    if (n == 1)
+        return 1;
+    return fibonacci(n - 1) + fibonacci(n - 2); // O(2^n), each call spawns two more recursive calls
+                                                // Could be optimised by using iteration instead of recursion
+                                                // For loop would be O(n) since it takes the previous number, adding
+                                                // current number, then stepping up until it has iterated n times
+                                                // Linear growth instead of exponential
+    // int current = 1;
+    // int previous = 0;
+    // for (int i = 2; i <= n; i++)
+    // {
+    //     int next = previous + current;
+    //     previous = current;
+    //     current = next;
+    // }
+    // return current;
+}
+
+int countOccurrences (const std::string& s, const char c)
+{
+    if (s.empty())
+        return 0;
+    const int count = (s[0] == c ? 1 : 0);
+    return count + countOccurrences(s.substr(1), c);
+    // O(n^2) since we have to make a new substring for every index of the original string
+}
+
+int findLargestElement(const int arr[], const int size)
+{
+    if (size <= 0)
+        return 0;
+    if (size == 1)
+        return arr[0];
+    const int mid = size / 2;
+    const int leftMax = findLargestElement(arr, mid);
+    const int rightMax = findLargestElement(arr + mid, size - mid);
+
+    return (leftMax > rightMax) ? leftMax : rightMax;
+    // O(n) time complexity, since we have to compare each element at least once
+}
+
+// Up to, not including, end
+void traverseAsciiTable(const char start, const char end)
+{
+    if (start >= end)
+        return;
+    std::cout << start << " ";      // Reflects the building
+    traverseAsciiTable(static_cast<char>(start + 1), end);
+
+    std::cout << " ";               // Reflects the unwinding
+}
+
+// Helper funcs to populate and randomise input
+
+void fillRandomArray(int arr[], const int size, const int minVal, const int maxVal)
+{
+    std::random_device rd;
+    std::mt19937 gen(rd());
+    std::uniform_int_distribution<> dist(minVal, maxVal);
+
+    for (int i = 0; i < size; i++)
+    {
+        arr[i] = dist(gen);
+    }
+}
+
+std::string makeRandomString(const int len, char minChar = 'a', char maxChar = 'z')
+{
+    if (len <= 0)
+        return{};
+    std::random_device rd;
+    std::mt19937 gen(rd());
+    std::uniform_int_distribution<int> dist(minChar, maxChar);
+
+    std::string s;
+    s.reserve(len);
+    for (int i = 0; i < len; i++)
+        s.push_back(static_cast<char>(dist(gen)));
+    return s;
+}
+
+int countOccurrences_index(const std::string& s, const char c, int index)
+{
+    if (index >= static_cast<int>(s.size()))
+        return 0;
+    const int hit = (s[index] == c ? 1 : 0);
+    return hit + countOccurrences_index(s, c, index + 1);
+}
+
+

Fundamental_Recursion/Utils.h

@@ -0,0 +1,33 @@
+#ifndef FUNDAMENTAL_RECURSION_UTILS_H
+#define FUNDAMENTAL_RECURSION_UTILS_H
+
+#include <string>
+#include <chrono>
+
+
+void printNaturalNumber(int n);
+int calculateFactorial(int n);
+int power(int base, int exp);
+int fibonacci(int n);
+int countOccurrences(const std::string& s, char c);
+int findLargestElement(const int arr[], int size);
+void traverseAsciiTable(char start, char end);
+
+
+// Helpers partially generated by ChatGPT
+void fillRandomArray(int arr[], int size, int minVal, int maxVal);
+std::string makeRandomString(int len, char minChar, char maxChar);
+int countOccurrences_index(const std::string& s, char c, int index);
+
+template<typename F, typename... Args>
+double time_ms(F&& f, Args&&... args)
+{
+    auto t0 = std::chrono::high_resolution_clock::now();
+    (void)std::forward<F>(f)(std::forward<Args>(args)...);
+    auto t1 = std::chrono::high_resolution_clock::now();
+    return std::chrono::duration<double, std::milli>(t1 - t0).count();
+}
+
+
+
+#endif //FUNDAMENTAL_RECURSION_UTILS_H

Fundamental_Recursion/main.cpp

@@ -0,0 +1,89 @@
+#include <chrono>
+#include <iostream>
+#include "Utils.h"
+
+static void line(const char* title)
+{
+    std::cout << "\n======= " << title << "=======\n";
+}
+
+int main()
+{
+    line("Neutral numbers");
+    printNaturalNumber(10);
+    std::cout << "\n";
+
+
+    line("Factorial");
+    const int fact_expect[] = {
+        1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800
+    };
+    bool ok_fact = true;
+    for (int n = 0; n <= 10; ++n) {
+        int r = calculateFactorial(n);
+        std::cout << "n=" << n << " -> " << r
+                  << (r == fact_expect[n] ? "  OK" : "  MISMATCH") << "\n";
+        ok_fact &= (r == fact_expect[n]);
+    }
+
+
+    line ("Power");
+    struct Case { int base, exp, expect; };
+    const Case pow_cases[] = {
+        {2,0,1}, {2,1,2}, {2,5,32}, {3,4,81}, {5,3,125}, {10,2,100}
+    };
+    bool ok_pow = true;
+    for (auto c : pow_cases) {
+        int r = power(c.base, c.exp);
+        std::cout << c.base << "^" << c.exp << " = " << r
+                  << (r == c.expect ? "  OK" : "  MISMATCH") << "\n";
+        ok_pow &= (r == c.expect);
+
+        line("Fibonacci");
+        const int fib_expect[] = {0,1,1,2,3,5,8,13,21,34,55,89,144};
+        bool ok_fib = true;
+        for (int n = 0; n <= 12; ++n) {
+            int r = fibonacci(n);
+            std::cout << "F(" << n << ") = " << r
+                      << (r == fib_expect[n] ? "  OK" : "  MISMATCH") << "\n";
+            ok_fib &= (r == fib_expect[n]);
+        }
+
+
+        line("Count occurrences");
+        std::string s = makeRandomString(2000, 'a', 'f');
+        char target = 'c';
+        int rec = countOccurrences(s, target);                                          //<--- recursive
+        int ref = static_cast<int>(std::count(s.begin(), s.end(), target));
+        std::cout << "recursive=" << rec << "  std::count=" << ref
+                  << (rec == ref ? "  OK" : "  MISMATCH") << "\n";
+        double t_rec_ms = time_ms([&]{ (void)countOccurrences(s, target); });
+        std::cout << "perf (recursive substr): ~" << t_rec_ms << " ms\n";
+
+
+        line ("Find largest element");
+        constexpr int N = 100000;
+        int* arr = new int[N];
+        fillRandomArray(arr, N, -100000, 100000);
+        double t_my_ms  = time_ms([&]{ (void)findLargestElement(arr, N); });
+        int myMax = findLargestElement(arr, N);
+        int stdMax = *std::max_element(arr, arr + N);
+        std::cout << "myMax=" << myMax << "  stdMax=" << stdMax
+                  << (myMax == stdMax ? "  OK" : "  MISMATCH") << "\n";
+        std::cout << "perf (recursive): ~" << t_my_ms << " ms\n";
+        delete[] arr;
+
+
+        line("Traverse Ascii table");
+        traverseAsciiTable('A', 'F');
+        std::cout << "\n";
+
+
+        line("Summary");
+        std::cout << "Factorial: " << (ok_fact ? "OK" : "FAIL") << "\n";
+        std::cout << "Power:     " << (ok_pow  ? "OK" : "FAIL") << "\n";
+        std::cout << "Fibonacci: " << (ok_fib  ? "OK" : "FAIL") << "\n";
+
+        return 0;
+    }
+}

assignment1/.idea/workspace.xml

@@ -29,15 +29,6 @@
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-      <change beforePath="$PROJECT_DIR$/TMovie.h" beforeDir="false" />
-      <change beforePath="$PROJECT_DIR$/TMovieList.cpp" beforeDir="false" />
-      <change beforePath="$PROJECT_DIR$/TMovieList.h" beforeDir="false" />
-      <change beforePath="$PROJECT_DIR$/TMovieNode.cpp" beforeDir="false" />
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@@ -91,11 +82,6 @@
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@@ -108,8 +94,8 @@
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     <list>
-      <item itemvalue="C/C++ File.main.cpp" />
       <item itemvalue="CMake Application.assignment1" />
+      <item itemvalue="C/C++ File.main.cpp" />
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@@ -123,6 +109,7 @@
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