added js 76-min-window

Author: anthonysim

javascript/76-Minimum-Window-Substring.js

@@ -0,0 +1,35 @@
+var minWindow = function (str, target) {
+  const hash = target.split('').reduce((acc, val) => {
+    if (!acc[val]) acc[val] = 0;
+    acc[val] += 1;
+    return acc;
+  }, {})
+
+  let start = 0;
+  let min = Infinity;
+  let matched = 0;
+  let subStringStart = null;
+
+  for (let i = 0; i < str.length; i++) {
+    let rightChar = str[i];
+
+    if (rightChar in hash) hash[rightChar] -= 1;
+    if (hash[rightChar] >= 0) matched += 1;
+
+    while (matched === target.length) {
+      if (i - start + 1 < min) {
+        subStringStart = start;
+        min = i - start + 1;
+      }
+
+      let leftChar = str[start];
+      start += 1;
+
+      if (leftChar in hash) {
+        if (hash[leftChar] === 0) matched -= 1;
+        hash[leftChar] += 1;
+      }
+    }
+  }
+  return min === Infinity ? '' : str.substring(subStringStart, subStringStart + min);
+};