feat: 最长回文串

src/leecode/No5.java

@@ -0,0 +1,32 @@
+package leecode;
+
+import java.util.Arrays;
+
+/**
+ * @author Wen
+ * @date 2025/6/20 21:54
+ */
+public class No5 {
+    public String longestPalindrome(String s) {
+        int size = s.length();
+        boolean[][] dp = new boolean[size][size];
+        for (int i = 0; i < size; i ++) {
+            Arrays.fill(dp[i], false);
+        }
+        int maxLen = 0;
+        String res = "";
+        // 如果dp[i+1][j-1]为回文串，那么字符串i位==字符串j位时，dp[i][j]也为回文串
+        for (int i = size - 1; i >= 0; i--) {
+            for (int j = i; j < size; j ++) {
+                if (s.charAt(i) == s.charAt(j) && (j - i <= 1 || dp[i+1][j-1])) {
+                    dp[i][j] = true;
+                    maxLen = Math.max(maxLen, j - i);
+                    if(j - i >= maxLen) {
+                        res = s.substring(i, j + 1);
+                    }
+                }
+            }
+        }
+        return res;
+    }
+}