字符串中查找最长回文子串完整代码

参考原文：http://blog.youkuaiyun.com/yzl_rex/article/details/7908259

#include <stdio.h>
#include <string.h>
#include <malloc.h>

int Min(int a,int b)
{
	return ((a-b)?b:a);
}

char* huiwen(char *s)
{
	if(NULL == s){
		return 0;
	}
	int id;
	int mx=0;
	int i=0;
	char *p;
	p = (char *)malloc(100);
	memset(p,0,sizeof(100));
	for(i=0;i<strlen(s);i++){
		if(mx>1){
			p[i] = Min(mx-i,p[2*id-i]);
		}else{
			p[i] = 1;
		}
		for(;s[i+p[i]]==s[i-p[i]];p[i]++);
		if(p[i]+i>mx){
			mx = p[i]+i;
			id = i;
		}
	}

	return p;
}

int findMax( char *s)
{
	if(s == NULL){
		return 0;
	}
	int max=0;
	int i=0;
	for(i=1;i<strlen(s);i++){
		if(s[i]>s[max]){
			max = i;
		}
	}
	return max;
}

int main(void)
{
//	char *s="1234321";
	
	int i=0;

	char *s;
	s = (char *)malloc(50);
	memset(s,0,10);
	scanf("%s",s);

	char *l;
	l = (char *)malloc(100);
	memset(l,0,100);
	*(l+i++)='$';
	char *d = s;
	while(*s != '\0'){
		*(l+i++) = '#';
		*(l+i++) = *s;
		s++;
	}
	*(l+i) = '#';

	char *p = huiwen(l);
	
	if(p == NULL){
		return -1;
	}

	printf("%s\n",l);
	for(i=0;p[i] != '\0';i++)
		printf("%d",p[i]);
	printf("\n");

	int max = findMax(p);
	int id = max/2 - 1;
	if(l[max] !='#'){
		for(i=id-(p[max]-1)/2;i<=id+(p[max]-1)/2;i++)
			printf("%c",d[i]);
	}else{
	      for(i=id-(p[max]-2)/2;i<=id+(p[max])/2;i++)
			printf("%c",d[i]);
	}
	printf("\n");
	free(p);
	free(l);
	free(d);
	return 0;
}

还有一种方法简单易懂，就是时间消耗更大，需要O（n*n）

#include <stdio.h>
#include <string.h>
#include <malloc.h>

char* huiwen(char *s)
{
	if(s == NULL){
		return NULL;
	}

	char *p;
	p = (char *)malloc(100);
	memset(p,0,100);

	int i,j;

	for(i=0;s[i] != '\0';i++){
		p[i]=1;
		if(s[i] != s[i+1]){
			for(j=1;i>=j && s[i+j] != '\0' && s[i-j] == s[i+j] ;j++){
				p[i]++;			
			}
		}else{
			p[i]=2;
			for(j=1;i>=j && s[i+j+1] != '\0' && s[i-j] == s[i+j+1] ;j++){
				p[i]++;			
			}
		}
	}

	return p;
}

int findMax( char *s)
{
	if(s == NULL){
		return 0;
	}
	int max=0;
	int i=0;
	for(i=1;i<strlen(s);i++){
		if(s[i]>s[max]){
			max = i;
		}
	}
	return max;
}

int main(void)
{
	char *s;
	s = (char *) malloc(100);
	memset(s,0,100);

	scanf("%s",s);

	char *p = huiwen(s);

	int i=0;
	while(p[i] != '\0'){
		printf("%d",p[i]);
		i++;
	}

	int max = findMax(p);
	//printf("%d\n", max);

	//printf("%s\n", s);

	if(s[max] != s[max+1]){
		for(i= max-(p[max]-1); i<= max+(p[max]-1);i++)
			printf("%c",s[i]);
	}else{
		for(i= max-p[max]+2;i<= max+1+(p[max]-1);i++){
			printf("%c",s[i]);

		}
	}
	printf("\n");

	free(s);
	free(p);

	return 0;
}