牛客网NOIP赛前集训营-提高组（第七场）C 洞穴

洞穴

思路:

矩阵乘法

由于只需要知道 A ^ l 的 第a行第b个元素

所以我们每次在做矩阵乘法时只需要算第a行就可以了

还要像矩阵快速幂一样预处理A ^ (1<<d)

代码:

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize(4)
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pi acos(-1.0)
#define LL long long
//#define mp make_pair
#define pb push_back
#define ls rt<<1, l, m
#define rs rt<<1|1, m+1, r
#define ULL unsigned LL
#define pll pair<LL, LL>
#define pli pair<LL, int>
#define pii pair<int, int>
#define piii pair<pli, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);
//head

const int N = ;
bool a[N][N][];
bool t[N][];
int main() {
    int n, m, u, v, q, l;
    scanf("%d %d", &n, &m);
    for (int i = ; i < m; i++) {
        scanf("%d %d", &u, &v);
        a[u][v][] = true;
    }
    for (int d = ; d <= ; d++) {
        for (int i = ; i <= n; i++) {
            for (int j = ; j <= n; j++) {
                if(a[i][j][d-])
                for (int k = ; k <= n; k++) {
                    if(a[j][k][d-]) {
                        a[i][k][d] = true;
                    }
                }
            }
        }
    }
    scanf("%d", &q);
    while(q--) {
        scanf("%d %d %d", &l, &u, &v);
        int now = ;
        for (int i = ; i <= n; i++) t[i][now] = ;
        t[u][now] = ;
        for (int i = ; i >= ; i--) {
            if(l&(<<i)) {
                now ^= ;
                for (int j = ; j <= n; j++) t[j][now] = ;
                for (int j = ; j <= n; j++) {
                    if(t[j][now^]) {
                        for (int k = ; k <= n; k++) {
                            if(a[j][k][i])
                                t[k][now] = ;
                        }
                    }
                }
            }
        }
        if(t[v][now]) puts("YES");
        else puts("NO");
    }
    return ;
}