UVaLA 3026 Period MP算法

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MP算法求失配函数

对于f [] 数组的定义如下：

 

　1) f[j] = 0  j = 0,1

 

　2) f[j] = max(k): 0<k<j   P[0...k-1]=P[j-k,j-1]

 

#include <cstdio>
#include <cstring>
#include <iostream>
using namespace std;

const int MAXN = 1000000 + 10;
char P[MAXN];
int n, f[MAXN];
//失配函数求 f 数组
void getFail()
{
    f[0] = f[1] = 0;        //递推边界初值
    for (int i = 1; i <= n; i++)
    {
        int j = f[i];
        while (j && P[i] != P[j]) j = f[j];
        f[i + 1] = P[i] == P[j] ? j + 1 : 0;
    }
}

int main()
{
    int kase = 0;
    while (~scanf("%d", &n) && n)
    {
        scanf("%s", P);
        getFail();

        printf("Test case #%d\n", ++kase);
        for (int i = 2; i <= n; i++)
            if (f[i] > 0 && i % (i - f[i]) == 0)
                printf("%d %d\n", i, i / (i - f[i]));

        printf("\n");
    }
    return 0;
}