【HDOJ】2157 How many ways??

矩阵乘法，用DP做各种wa，后来发现原因了。

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

typedef struct {
    int map[20][20];
} matrix_st;

matrix_st res, org;
int n, m;

matrix_st multiply(matrix_st a, matrix_st b) {
    int i, j, k;
    matrix_st c;

    for (i=0; i<n; ++i) {
        for (j=0; j<n; ++j) {
            c.map[i][j] = 0;
            for (k=0; k<n; ++k)
                c.map[i][j] += a.map[i][k] * b.map[k][j];
            c.map[i][j] %= 1000;
        }
    }

    return c;
}

void calc(matrix_st org, int k) {
    while (k) {
        if (k & 1)
            res = multiply(res, org);
        k >>= 1;
        org = multiply(org, org);
    }
}

int main() {
    int t, i, j, k;

    while (scanf("%d %d", &n, &m)!=EOF && (n||m)) {
        memset(org.map, 0, sizeof(org.map));
        for (i=0; i<m; ++i) {
            scanf("%d %d", &j, &k);
            org.map[j][k] = 1;
        }
        scanf("%d", &t);
        while (t--) {
            memset(res.map, 0, sizeof(res.map));
            for (i=0; i<n; ++i)
                res.map[i][i] = 1;
            scanf("%d %d %d", &i, &j, &k);
            calc(org, k);
            printf("%d\n", res.map[i][j]);
        }

    }

    return 0;
}