feat: implement sliding window algorithms for fixed and dynamic sizes with tests

Author: Kesavan-77

Diff for: Sliding-Windows/LongestSubarrayWithSumAtMost.js

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+/**
+ * Function to find the longest subarray with a sum <= target.
+ *
+ * @param {number[]} arr - The input array of numbers.
+ * @param {number} target - The target sum for the dynamic window.
+ * @returns {number} - The length of the longest subarray with a sum <= target.
+ */
+export function longestSubarrayWithSumAtMost(arr, target) {
+  let maxLength = 0
+  let windowSum = 0
+  let left = 0
+  for (let right = 0; right < arr.length; right++) {
+    windowSum += arr[right]
+    while (windowSum > target) {
+      windowSum -= arr[left]
+      left++
+    }
+    maxLength = Math.max(maxLength, right - left + 1)
+  }
+  return maxLength
+}

Diff for: Sliding-Windows/MaxSumSubarrayFixed.js

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+/**
+ * Function to find the maximum sum of a subarray of fixed size k.
+ *
+ * @param {number[]} arr - The input array of numbers.
+ * @param {number} k - The fixed size of the subarray.
+ * @returns {number} - The maximum sum of any subarray of size k.
+ * @throws {RangeError} - If k is larger than the array length or less than 1.
+ */
+export function maxSumSubarrayFixed(arr, k) {
+  if (k > arr.length || k < 1) {
+    throw new RangeError(
+      'Subarray size k must be between 1 and the length of the array'
+    )
+  }
+  let maxSum = 0
+  let windowSum = 0
+  for (let i = 0; i < k; i++) {
+    windowSum += arr[i]
+  }
+  maxSum = windowSum
+  for (let i = k; i < arr.length; i++) {
+    windowSum += arr[i] - arr[i - k]
+    maxSum = Math.max(maxSum, windowSum)
+  }
+  return maxSum
+}

Diff for: Sliding-Windows/test/LongestSubarrayWithSumAtMost.test.js

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+import { longestSubarrayWithSumAtMost } from '../LongestSubarrayWithSumAtMost'
+
+describe('Dynamic-size Sliding Window - longestSubarrayWithSumAtMost', () => {
+  it('should return the longest subarray length with sum <= target', () => {
+    const arr = [1, 2, 3, 4, 5]
+    const target = 7
+    const result = longestSubarrayWithSumAtMost(arr, target)
+    expect(result).toBe(3)
+  })
+
+  it('should return the full array length if the entire sum is within the target', () => {
+    const arr = [1, 1, 1, 1]
+    const target = 4
+    const result = longestSubarrayWithSumAtMost(arr, target)
+    expect(result).toBe(4)
+  })
+
+  it('should return 0 if no subarray meets the sum condition', () => {
+    const arr = [5, 6, 7]
+    const target = 3
+    const result = longestSubarrayWithSumAtMost(arr, target)
+    expect(result).toBe(0)
+  })
+})

Diff for: Sliding-Windows/test/MaxSumSubarrayFixed.test.js

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+import { maxSumSubarrayFixed } from '../MaxSumSubarrayFixed'
+
+describe('Fixed-size Sliding Window - maxSumSubarrayFixed', () => {
+  it('should return the maximum sum of a subarray of size k', () => {
+    const arr = [2, 1, 5, 1, 3, 2]
+    const k = 3
+    const result = maxSumSubarrayFixed(arr, k)
+    expect(result).toBe(9)
+  })
+
+  it('should throw a RangeError if k is larger than the array length', () => {
+    const arr = [2, 1, 5]
+    const k = 4
+    expect(() => maxSumSubarrayFixed(arr, k)).toThrow(RangeError)
+  })
+
+  it('should throw a RangeError if k is less than 1', () => {
+    const arr = [2, 1, 5]
+    const k = 0
+    expect(() => maxSumSubarrayFixed(arr, k)).toThrow(RangeError)
+  })
+})