BNUOJ 52516 Just A String

$KMP$。

枚举每一个后缀，去原串中进行匹配，每次匹配到原串到$i$位置的后缀与这次枚举的后缀的前缀，更新答案。

#include<bits/stdc++.h>
using namespace std;

int T;
char a[2010];
int len1,len2;
int nx[2010];
long long ans;

void getNext(int x)
{
    int j, k;
    j = x;
    k = x-1;
    nx[x] = x-1;
    while(j < len1)
        if(k == x-1 || a[j] == a[k])
            nx[++j] = ++k;
        else
            k = nx[k];

}

void KMP_Index(int x)
{
    int i = 0, j = x;
    getNext(x);

    while(i < len1 )
    {
        if(j == x-1 || a[i] == a[j])
        {
            if(j!=x-1)
            {
                long long B = (long long)(j-x+1);
                long long A = (long long)(i+1-B);
                long long C = (long long)(len2-B);
                ans=ans^(A*B*B*C);
            }
            i++;
            j++;

        }
        else j = nx[j];
    }
}

int main()
{
    scanf("%d",&T);
    while(T--)
    {
        scanf("%s",a);
        len1 = strlen(a);

        ans=0;
        for(int i=0; i<len1; i++)
        {
            len2 = len1-i;
            memset(nx,0,sizeof nx);
            KMP_Index(i);
        }
        printf("%lld
",ans);
    }
    return 0;
}