Added longest substring solution

Author: nhistory

longest-substring-without-repeating-characters/nhistory.js

@@ -0,0 +1,19 @@
+var lengthOfLongestSubstring = function (s) {
+  // Create map to store character from string
+  let map = new Map();
+  let maxLen = 0;
+  let start = 0;
+
+  for (let end = 0; end < s.length; end++) {
+    if (map.has(s[end])) {
+      // Move the start pointer to the right of the previous position of current character
+      start = Math.max(map.get(s[end]) + 1, start);
+    }
+    map.set(s[end], end);
+    maxLen = Math.max(maxLen, end - start + 1);
+  }
+  return maxLen;
+};
+
+// TC: O(n)
+// SC: O(n)