Added minimum window substring implementation and test file

Author: Mayank29903

Sliding-Windows/MinimumWindowSubstring.js

@@ -0,0 +1,42 @@
+/*
+ * Author: Mayank
+ * Minimum Window Substring implementation in JavaScript
+ * Finds the smallest substring of s that contains all characters of t.
+ */
+
+function minWindowSubstring(s, t) {
+  if (t.length > s.length) return ""
+
+  const need = {}
+  for (let char of t) {
+    need[char] = (need[char] || 0) + 1
+  }
+
+  let left = 0
+  let count = t.length
+  let minLen = Infinity
+  let minStart = 0
+
+  for (let right = 0; right < s.length; right++) {
+    if (need[s[right]] !== undefined) {
+      if (need[s[right]] > 0) count--
+      need[s[right]]--
+    }
+
+    while (count === 0) {
+      if (right - left + 1 < minLen) {
+        minLen = right - left + 1
+        minStart = left
+      }
+      if (need[s[left]] !== undefined) {
+        need[s[left]]++
+        if (need[s[left]] > 0) count++
+      }
+      left++
+    }
+  }
+
+  return minLen === Infinity ? "" : s.substring(minStart, minStart + minLen)
+}
+
+export { minWindowSubstring }

Sliding-Windows/test/MinimumWindowSubstring.test.js

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+/*
+ * Test file for Minimum Window Substring
+ */
+
+import { minWindowSubstring } from "../MinimumWindowSubstring.js"
+
+test("return smallest window containing all characters", () => {
+  expect(minWindowSubstring("ADOBECODEBANC", "ABC")).toBe("BANC")
+})
+
+test("return empty string if no window found", () => {
+  expect(minWindowSubstring("HELLO", "XYZ")).toBe("")
+})
+
+test("return full string if it matches exactly", () => {
+  expect(minWindowSubstring("ABC", "ABC")).toBe("ABC")
+})