Vijos1603 迷宫

题目链接：https://vijos.org/p/1603

矩阵快速幂，答案是原矩阵的m次幂的第s行第f列

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#define rep(i,l,r) for(int i=l; i<=r; i++)
#define clr(x,y) memset(x,y,sizeof(x))
using namespace std;
const int maxn = 51;
int n,m,s,f,KPM;
struct matrix{
    int m[maxn][maxn];
    matrix(){
        clr(m,0);
    }
    void init(){
        rep(i,1,n) m[i][i] = 1;
    }
    matrix operator * (const matrix &y) const {
        matrix ret;
        rep(i,1,n) rep(j,1,n) rep(k,1,n)
        ret.m[i][j] = (ret.m[i][j] + m[i][k] * y.m[k][j]) % KPM;
        return ret;
    }
}a;
inline int read(){
    int ans = 0, f = 1;
    char c = getchar();
    while (!isdigit(c)){
        if (c == '-') f = -1;
        c = getchar();
    }
    while (isdigit(c)){
        ans = ans * 10 + c - '0';
        c = getchar();
    }
    return ans * f;
}
matrix qpow(matrix x,int y){
    matrix ret, b = x; ret.init();
    while (y){
        if (y & 1) ret = ret * b;
        b = b * b;
        y >>= 1;
    }
    return ret;
}
int main(){
    n = read();
    rep(i,1,n) rep(j,1,n) a.m[i][j] = read();
    m = read(); s = read(); f = read(); KPM = read();
    a = qpow(a,m);
    printf("%d
",a.m[s][f]);
    return 0;
}