dev/leetcode/longestpalindromicsubstring

Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: “babad”
Output: “bab”
Note: “aba” is also a valid answer.

Example 2:

Input: “cbbd”
Output: “bb”

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public class Solution {

public String longestPalindrome(String s) {
int len = s.length();
if (len < 2) {
return s;
}

boolean[][] dp = new boolean[len][len];

// 初始化
for (int i = 0; i < len; i++) {
dp[i][i] = true;
}

int maxLen = 1;
int start = 0;

for (int j = 1; j < len; j++) {
for (int i = 0; i < j; i++) {

if (s.charAt(i) == s.charAt(j)) {
if (j - i < 3) {
dp[i][j] = true;
} else {
dp[i][j] = dp[i + 1][j - 1];
}
} else {
dp[i][j] = false;
}

// 只要 dp[i][j] == true 成立,就表示子串 s[i, j] 是回文,此时记录回文长度和起始位置
if (dp[i][j]) {
int curLen = j - i + 1;
if (curLen > maxLen) {
maxLen = curLen;
start = i;
}
}
}
}
return s.substring(start, start + maxLen);
}
}

Reference
https://leetcode-cn.com/problems/longest-palindromic-substring