字符串中查找最长回文子串完整代码

参考原文：http://blog.csdn.net/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;
}