开关问题

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
#define maxn 50
int a[maxn][maxn], length, ans[maxn];

void Gauss()
{
    int i, j, k, r, col;
    for(k = 0, col = 0; k < length&&col < length; k++, col++)
    {
        int i = k;
        while(i < length&&a[i][col] == 0) i++;
        if(a[i][col] == 0)
        {
            k--;
            continue;
        }
        if(i > k)
        {
            for(r = col; r <= length; r++)
            {
                swap(a[i][r], a[k][r]);
            }
        }
        for(i = k+1; i < length; i++)
        {
            if(a[i][col])
            {
                for(j = col; j <= length; j++)
                    a[i][j] ^= a[k][j];
            }
        }
    }
    for(i = k; i <length; i++)
    {
        if(a[i][length] != 0)
        {
            printf("Oh,it‘s impossible~!!\n");
            return;
        }
    }
    printf("%d\n",(1 << (length - k)));
    return;
}

int main()
{
    int i, T;
    scanf("%d", &T);
    while(T--)
    {
        memset(a, 0, sizeof(a));
        scanf("%d",&length);
        for(i = 0; i < length; i++)
        {
            scanf("%d", &a[i][length]);
            a[i][i] = 1;
        }
        int x;
        for(i = 0; i <length; i++)
        {
            scanf("%d", &x);
            a[i][length] = a[i][length]^x;
        }
        int m, n;
        while(~scanf("%d %d", &m, &n))
        {
            if(m+n == 0) break;
            a[n-1][m-1] = 1;
        }
        Gauss();
    }
    return 0;
}