AcWing

https://www.acwing.com/problem/content/210/

要注意两点：开关之间的关系不一定是对称的，并且每个开关会控制自己。

消元的过程中可以计算出矩阵的秩，假如某个行没有主元但是有常数，那么就直接-1了。

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

const int MAXN = 40;

bool a[MAXN + 5][MAXN + 1 + 5 ];
bool ans[MAXN + 5];

int Gauss_Jordan(int n) {
    int r = 0;
    for(int i = 1; i <= n; ++i) {
        int mx = i;
        for(int j = i; j <= n; ++j) {
            if(a[j][i]) {
                mx = j;
                break;
            }
        }

        if(!a[mx][i])
            continue;

        ++r;
        if(mx != i) {
            for(int j = 1; j <= n + 1; ++j)
                swap(a[i][j], a[mx][j]);
        }

        for(int j = 1; j <= n + 1; ++j) {
            if(j != i && a[j][i]) {
                for(int k = 1; k <= n + 1; ++k)
                    a[j][k] ^= a[i][k];
            }
        }
    }
    for(int i = 1; i <= n; ++i) {
        if(a[i][i] == 0 && a[i][n + 1])
            return -1;
    }

    /*for(int i = 1; i <= n; ++i) {
        for(int j = 1; j <= n + 1; ++j) {
            printf(" %d", (int)a[i][j]);
        }
        printf("
");
    }
    puts("---
");*/

    for(int i = 1; i <= n; ++i)
        ans[i] = a[i][n + 1] & a[i][i];
    return r;
}

int main() {
#ifdef Yinku
    freopen("Yinku.in", "r", stdin);
#endif // Yinku
    int T;
    scanf("%d", &T);
    while(T--) {
        memset(a, 0, sizeof(a));
        int n;
        scanf("%d", &n);
        for(int i = 1, x; i <= n; ++i) {
            scanf("%d", &x);
            a[i][n + 1] = x;
        }
        for(int i = 1, x; i <= n; ++i) {
            scanf("%d", &x);
            a[i][n + 1] ^= x;
        }
        for(int i = 1; i <= n; ++i)
            a[i][i] = 1;

        int i, j;
        do {
            scanf("%d%d", &i, &j);
            if(i == 0 && j == 0)
                break;
            a[j][i] = 1;
        } while(1);

        /*for(int i = 1; i <= n; ++i) {
            for(int j = 1; j <= n + 1; ++j) {
                printf(" %d", (int)a[i][j]);
            }
            printf("
");
        }
        puts("---
");*/

        int r = Gauss_Jordan(n);
        if(r == -1)
            puts("Oh,it's impossible~!!");
        else
            printf("%lld
", 1ll << (n - r));
    }
}