1 Star 0 Fork 3

buelev / leetcode

forked from 光花梗虎耳草 / leetcode 
加入 Gitee
与超过 1200万 开发者一起发现、参与优秀开源项目,私有仓库也完全免费 :)
免费加入
克隆/下载
README.md 5.01 KB
一键复制 编辑 原始数据 按行查看 历史

5. 最长回文子串

English Version

题目描述

给你一个字符串 s,找到 s 中最长的回文子串。

 

示例 1:

输入:s = "babad"
输出:"bab"
解释:"aba" 同样是符合题意的答案。

示例 2:

输入:s = "cbbd"
输出:"bb"

示例 3:

输入:s = "a"
输出:"a"

示例 4:

输入:s = "ac"
输出:"a"

 

提示:

  • 1 <= s.length <= 1000
  • s 仅由数字和英文字母(大写和/或小写)组成

解法

动态规划法。

dp[i][j] 表示字符串 s[i..j] 是否为回文串。

  • j - i < 2,即字符串长度为 2 时,只要 s[i] == s[j]dp[i][j] 就为 true。
  • j - i >= 2dp[i][j] = dp[i + 1][j - 1] && s[i] == s[j]

Python3

class Solution:
    def longestPalindrome(self, s: str) -> str:
        n = len(s)
        dp = [[False] * n for _ in range(n)]
        start, mx = 0, 1
        for j in range(n):
            for i in range(j + 1):
                if j - i < 2:
                    dp[i][j] = s[i] == s[j]
                else:
                    dp[i][j] = dp[i + 1][j - 1] and s[i] == s[j]
                if dp[i][j] and mx < j - i + 1:
                    start, mx = i, j - i + 1
        return s[start:start + mx]

Java

class Solution {
    public String longestPalindrome(String s) {
        int n = s.length();
        boolean[][] dp = new boolean[n][n];
        int mx = 1, start = 0;
        for (int j = 0; j < n; ++j) {
            for (int i = 0; i <= j; ++i) {
                if (j - i < 2) {
                    dp[i][j] = s.charAt(i) == s.charAt(j);
                } else {
                    dp[i][j] = dp[i + 1][j - 1] && s.charAt(i) == s.charAt(j);
                }
                if (dp[i][j] && mx < j - i + 1) {
                    mx = j - i + 1;
                    start = i;
                }
            }
        }
        return s.substring(start, start + mx);
    }
}

C++

class Solution {
public:
    string longestPalindrome(string s) {
        int n = s.size();
        vector<vector<bool>> dp(n, vector<bool>(n, false));
        int start = 0, mx = 1;
        for (int j = 0; j < n; ++j) {
            for (int i = 0; i <= j; ++i) {
                if (j - i < 2) {
                    dp[i][j] = s[i] == s[j];
                } else {
                    dp[i][j] = dp[i + 1][j - 1] && s[i] == s[j];
                }
                if (dp[i][j] && mx < j - i + 1) {
                    start = i;
                    mx = j - i + 1;
                }
            }
        }
        return s.substr(start, mx);
    }
};

Go

func longestPalindrome(s string) string {
	n := len(s)
	dp := make([][]bool, n)
	for i := 0; i < n; i++ {
		dp[i] = make([]bool, n)
	}
	mx, start := 1, 0
	for j := 0; j < n; j++ {
		for i := 0; i <= j; i++ {
			if j-i < 2 {
				dp[i][j] = s[i] == s[j]
			} else {
				dp[i][j] = dp[i+1][j-1] && s[i] == s[j]
			}
			if dp[i][j] && mx < j-i+1 {
				mx, start = j-i+1, i
			}
		}
	}
	return s[start : start+mx]
}

C#

public class Solution{
    public string LongestPalindrome(string s) {
        int n = s.Length;
        bool[,] dp = new bool[n, n];
        int mx = 1, start = 0;
        for (int j = 0; j < n; ++j)
        {
            for (int i = 0; i <= j; ++i)
            {
                if (j - i < 2)
                {
                    dp[i, j] = s[i] == s[j];
                }
                else
                {
                    dp[i, j] = dp[i + 1, j - 1] && s[i] == s[j];
                }
                if (dp[i, j] && mx < j - i + 1)
                {
                    mx = j - i + 1;
                    start = i;
                }
            }
        }
        return s.Substring(start, mx);
    }
}

Nim

import std/sequtils

proc longestPalindrome(s: string): string =
  let n: int = s.len()
  var
    dp = newSeqWith[bool](n, newSeqWith[bool](n, false))
    start: int = 0
    mx: int = 1

  for j in 0 ..< n:
    for i in 0 .. j:
      if j - i < 2:
        dp[i][j] = s[i] == s[j]
      else:
        dp[i][j] = dp[i + 1][j - 1] and s[i] == s[j]

      if dp[i][j] and mx < j - i + 1:
        start = i
        mx = j - i + 1

  result = s[start ..< start+mx]

...

马建仓 AI 助手
尝试更多
代码解读
代码找茬
代码优化
1
https://gitee.com/buelev/leetcode.git
git@gitee.com:buelev/leetcode.git
buelev
leetcode
leetcode
main

搜索帮助

344bd9b3 5694891 D2dac590 5694891