next数组的应用，假设字符串长度为len，则next[len]的值为整个字符串的最长前后缀的长度。
len - next[len]即为题目所求p
#include<stdio.h>
#include<string.h>
const int maxn = 1e6+10;
char s[maxn];
int len,next[maxn];
int ans[maxn];
void getNext()
{
next[0] = -1;
int i = 0,j = -1;
while(i < len)
{
if(j == -1 || s[i] == s[j])
next[++i] = ++j;
else j = next[j];
}
}
int main()
{
int T,cas = 0;
scanf("%d",&T);
while(T--)
{
int as = 0;
scanf("%s",s);
len = strlen(s);
getNext();
int tmp = next[len];
int i = 0;
while(tmp > 0)
{
ans[i++] = len - tmp;
tmp = next[tmp];
as++;
}
printf("Case #%d: %d\n",++cas,++as);
for(int j = 0;j < i;j++)
printf("%d ",ans[j]);
printf("%d\n",len);
}
return 0;
}