Add minimum-window-substring solution

Author: Jeehay28

minimum-window-substring/Jeehay28.js

@@ -0,0 +1,63 @@
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {string}
+ */
+
+// 🚀 sliding window + two pointer approach
+
+// 🕒 Time Complexity: O(n), where n is the length of s
+// The inner while loop shrinks the window from the left side but never exceeds the total number of characters in s
+
+// 🗂 Space Complexity: O(m) (or worst case O(n)), where n is the length of t
+
+var minWindow = function (s, t) {
+  // early return for the critical edge case
+  if (s.length < t.length) {
+    return "";
+  }
+
+  let windowCnt = new Map();
+  let charCnt = new Map();
+  let minStart = 0;
+  let minEnd = s.length; // set this to an out-of-bounds value initially
+
+  let formed = 0;
+  let left = 0;
+
+  // initialize charCount
+  // 🔢 t = "ABC", charCount = { A: 1, B: 1, C: 1 }
+  for (const ch of t) {
+    charCnt.set(ch, (charCnt.get(ch) || 0) + 1);
+  }
+
+  // expand the windowCnt
+  for (let right = 0; right < s.length; right++) {
+    const char = s[right];
+
+    windowCnt.set(char, (windowCnt.get(char) || 0) + 1);
+
+    if (charCnt.has(char) && charCnt.get(char) === windowCnt.get(char)) {
+      formed += 1;
+    }
+
+    // shrink the window by moving the left pointer
+    while (formed === charCnt.size) {
+      if (right - left < minEnd - minStart) {
+        minStart = left;
+        minEnd = right;
+      }
+
+      const char = s[left];
+      windowCnt.set(char, windowCnt.get(char) - 1);
+
+      if (charCnt.has(char) && windowCnt.get(char) < charCnt.get(char)) {
+        formed -= 1;
+      }
+      left += 1;
+    }
+  }
+
+  return minEnd === s.length ? "" : s.slice(minStart, minEnd + 1);
+};
+