leetcode算法题练习--最长回文子串（c语言）

1、问题描述

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”
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/longest-palindromic-substring
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第一种方法：动态规划

参考如下文章
https://leetcode-cn.com/problems/longest-palindromic-substring/solution/zhong-xin-kuo-san-dong-tai-gui-hua-by-liweiwei1419/

char * longestPalindrome(char * s){
    char d[1000][1000] ={0};
    int i,j,curlen,start=0,maxlen=1;
    int length = strlen(s);
    for(j=1; j<length; j++){
        for(i=0; i<j; i++){
            if(s[i]==s[j])
                if(j-i<3)
                    d[i][j] = 1;
                else
                    d[i][j] = d[i+1][j-1];
            if(d[i][j]){
                curlen = j-i+1;
                if(curlen > maxlen){
                    maxlen = curlen;
                    start = i;
                }
            }
        }
    }
    if(length==0)
        maxlen = 0;
    *(s+start+maxlen) = 0;
    return s+start;
}

第二种方法：中心扩散法

void longestPart(char* s, int length, int left, int right, int* maxlen, int* start){
    int curlen;
    while(left >=0 && right<length){
            if(s[left]==s[right]){
                curlen =right-left+1;
                if(curlen > *maxlen){
                    *maxlen = curlen;
                    *start = left;
                }
                left--;
                right++;
            }
            else
                break;
            
    }
}
char * longestPalindrome(char * s){
    int i,start=0,maxlen=1;
    int length = strlen(s);
    for(i=0; i<length; i++){
        longestPart(s,length,i-1,i+1,&maxlen,&start);
    }
    for(i=0; i<length; i++){
        longestPart(s,length,i,i+1,&maxlen,&start);
    }   
    if(length==0)
        maxlen=0;  
    *(s+start+maxlen) = 0;