up code recursive function for factorial number problem

Author: sangtrandev00

src/algorithm/recursion/recursion-factorial.test.ts

@@ -0,0 +1,36 @@
+import { test, expect, describe } from 'bun:test';
+import { findFactorialRecursive, findFactorialIterative } from './recursion-factorial';
+
+describe('Factorial Functions', () => {
+    // Test cases for both recursive and iterative implementations
+    const testCases = [
+        { input: 0, expected: 1 },   // Edge case: 0! = 1
+        { input: 1, expected: 1 },   // Edge case: 1! = 1
+        { input: 5, expected: 120 }, // Normal case: 5! = 120
+        { input: 7, expected: 7 * 6 * 5 * 4 * 3 * 2 * 1 } // Larger number
+    ];
+
+    // Test recursive implementation
+    test('findFactorialRecursive handles various inputs', () => {
+        testCases.forEach(({ input, expected }) => {
+            expect(findFactorialRecursive(input)).toBe(expected);
+        });
+    });
+
+    // Test iterative implementation
+    test('findFactorialIterative handles various inputs', () => {
+        testCases.forEach(({ input, expected }) => {
+            expect(findFactorialIterative(input)).toBe(expected);
+        });
+    });
+
+    // Error and edge case handling
+    test('findFactorialRecursive handles negative numbers', () => {
+        expect(findFactorialRecursive(-1)).toBeUndefined();
+    });
+
+    test('findFactorialIterative handles negative numbers', () => {
+        expect(findFactorialIterative(-1)).toBeUndefined;
+    });
+
+});

src/algorithm/recursion/recursion-factorial.ts

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+// Write two functions that finds the factorial of any number. One should use recursive, the other should just use a for loop
+
+export function findFactorialRecursive(number: number): number | undefined {
+    if (number < 0) return undefined
+    // Stop point
+    if (number <= 1) return 1
+    //code here
+    return number * (findFactorialRecursive(number - 1) as number); // Recursive case
+    // return when need
+}
+// VD: 5! = 5 * 4 * 3 * 2 * 1 => 120 = 5 * 4 * 3 * 2 * 1
+// Step 1: number = 5 -> return 5 * func(4)
+// Step 2: number = 4 -> return 4 * func(3)
+// Step 3: number = 3 -> return 3 * func(2)
+// Step 4: number = 2 -> return 2 * func(1) // 1
+// Step 5: number = 1 -> return 1
+
+export function findFactorialIterative(number: number) {
+    if (number < 0) return undefined
+    if (number <= 1) return 1
+    let factorial = 1;
+    //code here
+    while (number > 1) {
+        factorial *= number
+        number -= 1
+    }
+    return factorial;
+}
+
+// 5
+// number = 4
+// 5 * 4
+// 5 * 4 * 3
+// 5 * 4 * 3 * 2