005Longest Palindromic Substring （C）

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.

开始竟然看成最大的逆序子串了

回文数有两种情况

（例）

1.abba

2.abgba

char* longestPalindrome(char* s) {
    int i=0,k,count,countmax[2],flag=0,start,end;
	if(s[i]=='\0'){
		return NULL;
	}
	if(s[i+1]=='\0'){
		return s;
	}
	count=countmax[0]=0;
	while(s[i+1]!='\0'){
		if(s[i]==s[i+1]){
			k=0;
			count=0;
			while(i-k>=0&&s[i+1+k]!='\0'&&s[i-k]==s[i+1+k]){
				k++;
				count+=2;
			}
		}
		if(count>countmax[0]){
			countmax[0]=count;
			countmax[1]=i;
		}
		i++;
	}
	for(i=0;s[i+2]!='\0';i++){
		if(s[i]==s[i+2]){
			k=0;
			count=1;
			while(i-k>=0&&s[i+2+k]!='\0'&&s[i-k]==s[i+2+k]){
				k++;
				count+=2;
			}
		}
		if(count>countmax[0]){
			countmax[0]=count;
			countmax[1]=i+1;
			flag=1;
		}
	}
	start=end=countmax[1];
	for(i=0;i<countmax[0]/2;i++){
		if(flag==0){
			end++;
			flag=1;
		}
		else{
			start--;
			end++;
		}
	}
	for(i=0;start+i<=end;i++){
		s[i]=s[start+i];
	}
	s[i]='\0';
	return s;
}