Longest Palindromic Substring

Author: TonyKim9401

longest-palindromic-substring/TonyKim9401.java

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+// TC: O(n^2)
+// for loop & nested while loop => total O(n^2)
+// SC: O(1)
+// uses only constant space => O(1)
+class Solution {
+    public String longestPalindrome(String s) {
+        int right = 0;
+        int left = 0;
+
+        for (int i = 0; i < s.length(); i++) {
+            int even = pad(s, i, i);
+            int odd = pad(s, i, i+1);
+            int max = Math.max(even, odd);
+
+            if (max > (right - left)) {
+                right = i + (max + 1) / 2;
+                left = i - max / 2;
+            }
+        }
+
+        return s.substring(left, right+1);
+    }
+
+    private int pad(String s, int start, int end) {
+        while (start >= 0 && end < s.length() && s.charAt(start) == s.charAt(end)) {
+            start -= 1;
+            end += 1;
+        }
+        return start - end;
+    }
+}