[LeetCode]-algorithms-Longest Palindromic Substring

Posted 2020-06-30 练子

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

and there exists one unique longest palindromic substring.

要求：给定一个字符串，求最长的回文字符串

"a"
=>a
"runcodes"
=>r
"runcodestatus"
=>tat
"runcodestats"
=>stats

public String longestPalindrome(String s) {
        s = s.trim();
        if(null==s || "".equals(s))
            return null;
        String res = s.substring(0,1);
        String temp;
        for(int i=0; i<s.length()-1; i++){
            temp = search(s, i, i);
            if(temp.length()>res.length())
                res = temp;
            temp = search(s, i, i+1);
            if(temp.length()>res.length())
                res = temp;
        }
        return res;
    }
    //这个方法向 i 的两端发散
    public String search(String s,int begin,int end){
        while(begin>=0 && end<s.length() && (s.charAt(begin)==s.charAt(end))){
            begin--;
            end++;
        }
        return s.substring((begin+1),end);
    }

分析：以每个字符为中心，遍历前后的字符串