Add longest-palindromic-substring solution in TS

Author: Jeehay28

longest-palindromic-substring/Jeehay28.ts

@@ -0,0 +1,26 @@
+// TC: O(n^2)
+// SC: O(1)
+function longestPalindrome(s: string): string {
+  if (s.length < 2) return s;
+
+  let maxLeft = 0;
+  let maxRight = 0;
+
+  const expandWindow = (left: number, right: number): void => {
+    while (left >= 0 && right < s.length && s[left] === s[right]) {
+      if (maxRight - maxLeft < right - left) {
+        maxRight = right;
+        maxLeft = left;
+      }
+      left--;
+      right++;
+    }
+  };
+
+  for (let i = 0; i < s.length; i++) {
+    expandWindow(i, i); // odd length palindrome
+    expandWindow(i, i + 1); // even length palindrome
+  }
+
+  return s.slice(maxLeft, maxRight + 1);
+}