fix: remove potential segmentation fault from factorial_memoization.cpp (#2994)

math/factorial_memoization.cpp

@@ -1,73 +1,65 @@
 /**
  * @file
- * @brief [Factorial](https://en.wikipedia.org/wiki/Factorial) calculation using recursion and [memoization](https://en.wikipedia.org/wiki/Memoization) 
+ * @brief [Factorial](https://en.wikipedia.org/wiki/Factorial) calculation using
+ * recursion and [memoization](https://en.wikipedia.org/wiki/Memoization)
  * @details
  * This program computes the factorial of a non-negative integer using recursion
- * with memoization (top-down dynamic programming). It stores intermediate results
- * to avoid redundant calculations for improved efficiency.
- * 
- * Memoization is a form of caching where the result to an expensive function call
- * is stored and returned.
- * Example:
- * Input: n = 5
- * Output: 120
- * 
+ * with memoization (top-down dynamic programming). It stores intermediate
+ * results to avoid redundant calculations for improved efficiency.
+ *
+ * Memoization is a form of caching where the result to an expensive function
+ * call is stored and returned. Example: Input: n = 5 Output: 120
+ *
  * Explanation: 5! = 5 × 4 × 3 × 2 × 1 = 120
- * 
- * The program uses a recursive function fact_recursion which caches computed 
- * results in a memo array to avoid recalculating factorials for the same numbers.
+ *
+ * The program uses a recursive function which caches computed
+ * results in a memo array to avoid recalculating factorials for the same
+ * numbers.
  *
  * Time Complexity: O(n)
  * Space Complexity: O(n)
- * @author [Vedant Mukhedkar](https://github.com/git5v)
  */
 
-#include <iostream> // for std::cout
 #include <cassert>  // For test cases
-#include <array>    // For std::array
 #include <cstdint>  // For uint64_t
+#include <vector>   // For std::vector
 
-/// Array to store computed factorials for memoization
-std::array<uint64_t, 1000> memo{0};
+class MemorisedFactorial {
+    std::vector<std::uint64_t> known_values = {1};
 
-/**
- * @namespace math
- * @brief Math algorithms
- */
-namespace math {
+ public:
+    /**
+     * @note This function was intentionally written as recursive
+     * and it does not handle overflows.
+     * @returns factorial of n
+     */
+    std::uint64_t operator()(std::uint64_t n) {
+        if (n >= this->known_values.size()) {
+            this->known_values.push_back(n * this->operator()(n - 1));
+        }
+        return this->known_values.at(n);
+    }
+};
 
-/**
- * @brief Computes the factorial of a non-negative integer using recursion and memoization.
- * @param n The integer whose factorial is to be computed
- * @returns The factorial of n
- */
-uint64_t fact_recursion(uint64_t n) {
-    if (n == 0) return 1;        // Base case: 0! = 1
-    if (memo[n] != 0) return memo[n]; // Return already computed value
-    memo[n] = n * fact_recursion(n - 1);    // Store and return the computed value
-    return memo[n];
+void test_MemorisedFactorial_in_order() {
+    auto factorial = MemorisedFactorial();
+    assert(factorial(0) == 1);
+    assert(factorial(1) == 1);
+    assert(factorial(5) == 120);
+    assert(factorial(10) == 3628800);
 }
 
-} // namespace math
-/**
- * @brief Self-test implementations for the fact_recursion function.
- * @returns void
- */
-void test_fact_recursion() {
-    // Test cases for factorial computation
-    assert(math::fact_recursion(0) == 1);
-    assert(math::fact_recursion(1) == 1);
-    assert(math::fact_recursion(5) == 120);
-    assert(math::fact_recursion(10) == 3628800);
-    std::cout << "All test cases passed!\n";
+void test_MemorisedFactorial_no_order() {
+    auto factorial = MemorisedFactorial();
+    assert(factorial(10) == 3628800);
 }
 
 /**
- * @brief Main function to run test cases and interact with the user.
+ * @brief Main function to run tests
  * @returns 0 on program success
  */
 int main() {
-    // Run test cases
-    test_fact_recursion();
+    test_MemorisedFactorial_in_order();
+    test_MemorisedFactorial_no_order();
     return 0;
 }