add: LongestPalindromeInAString

Author: Jer3myYu

java/Dynamic Programming/LongestPalindromeInAString.java

@@ -0,0 +1,40 @@
+public class LongestPalindromeInAString {
+    public String longestPalindromeInAString(String s) {
+        int n = s.length();
+        if (n == 0) {
+            return "";
+        }
+        boolean[][] dp = new boolean[n][n];
+        int maxLen = 1;
+        int startIndex = 0;
+        // Base case: a single character is always a palindrome.
+        for (int i = 0; i < n; i++) {
+            dp[i][i] = true;
+        }
+        // Base case: a substring of length two is a palindrome if both
+        // characters are the same.
+        for (int i = 0; i < n - 1; i++) {
+            if (s.charAt(i) == s.charAt(i + 1)) {
+                dp[i][i + 1] = true;
+                maxLen = 2;
+                startIndex = i;
+            }
+        }
+        // Find palindromic substrings of length 3 or greater.
+        for (int substringLen = 3; substringLen < n + 1; substringLen++) {
+            // Iterate through each substring of length 'substringLen'.
+            for (int i = 0; i < n - substringLen + 1; i++) {
+                int j = i + substringLen - 1;
+                // If the first and last characters are the same, and the
+                // inner substring is a palindrome, then the current
+                // substring is a palindrome.
+                if (s.charAt(i) == s.charAt(j) && dp[i + 1][j - 1]) {
+                    dp[i][j] = true;
+                    maxLen = substringLen;
+                    startIndex = i;
+                }
+            }
+        }
+        return s.substring(startIndex, startIndex + maxLen);
+    }
+}