Feat: 5. Longest Palindromic Substring

Author: HC-kang

longest-palindromic-substring/HC-kang.ts

@@ -0,0 +1,32 @@
+/**
+ * https://leetcode.com/problems/longest-palindromic-substring
+ * T.C. O(n^2)
+ * S.C. O(1)
+ */
+function longestPalindrome(s: string): string {
+  if (s.length < 2) return s;
+  let start = 0;
+  let end = 0;
+
+  for (let i = 0; i < s.length; i++) {
+    const len1 = expandBothSides(s, i, i); // odd
+    const len2 = expandBothSides(s, i, i + 1); // even
+    const len = Math.max(len1, len2);
+
+    if (len > end - start) {
+      start = i - Math.floor((len - 1) / 2);
+      end = i + Math.floor(len / 2);
+    }
+  }
+
+  return s.slice(start, end + 1);
+}
+
+function expandBothSides(s: string, left: number, right: number): number {
+  while (0 <= left && right < s.length && s[left] === s[right]) {
+    left--;
+    right++;
+  }
+
+  return right - left - 1;
+}