fix: handle empty array in maximumNonAdjacentSum

The empty-input guard was 'if (nums.length < 0) return 0', but length is
never negative, so it was dead code. For [] the function then read
nums[0] (undefined) and returned Math.max(0, undefined) === NaN instead
of 0. Change the guard to 'nums.length === 0' and add a test file.

Author: Shaked Shlomo

Dynamic-Programming/MaxNonAdjacentSum.js

@@ -5,7 +5,7 @@ function maximumNonAdjacentSum(nums) {
    * :return: The maximum non-adjacent sum
    */
 
-  if (nums.length < 0) return 0
+  if (nums.length === 0) return 0
 
   let maxIncluding = nums[0]
   let maxExcluding = 0

Dynamic-Programming/tests/MaxNonAdjacentSum.test.js

@@ -0,0 +1,21 @@
+import { maximumNonAdjacentSum } from '../MaxNonAdjacentSum'
+
+describe('maximumNonAdjacentSum', () => {
+  it('should return 0 for an empty array', () => {
+    expect(maximumNonAdjacentSum([])).toBe(0)
+  })
+
+  it('should return the single element for a one-element array', () => {
+    expect(maximumNonAdjacentSum([5])).toBe(5)
+  })
+
+  it('should compute the maximum non-adjacent sum', () => {
+    expect(maximumNonAdjacentSum([1, 2, 3])).toBe(4)
+    expect(maximumNonAdjacentSum([1, 5, 3, 7, 2, 2, 6])).toBe(18)
+    expect(maximumNonAdjacentSum([499, 500, -3, -7, -2, -2, -6])).toBe(500)
+  })
+
+  it('should return 0 when all elements are negative', () => {
+    expect(maximumNonAdjacentSum([-1, -5, -3, -7, -2, -2, -6])).toBe(0)
+  })
+})