【P2447 [SDOI2010]外星千足虫】 题解

题目链接:https://www.luogu.org/problemnew/show/P2447

dalao们都说简单...解异或方程组

可我不是dalao qwq

#include <algorithm>
#include <cstdio>
#include <cmath>
#include <iostream>
#include <bitset>
using namespace std;
const int maxn = 2500;
const double eps = 1e-7;
char s[maxn];
bitset<maxn> A[maxn];
int n, m, ans[maxn], flag;
bool check;
int main() 
{
    scanf("%d%d",&n,&m);
    for(int i = 1; i <= m; i++)
    {
        scanf("%s",s+1);
        for(int j = 1; j <= n; j++)
        A[i][j] = s[j]-'0';
        int p;
        scanf("%d",&p);
        A[i][n+1] = p;
    }
    for(int i = 1; i <= n; i++)
    {
        int p = i;
        while(p < m+1 && !A[p][i]) p++;
        if(p == m+1) 
        {
            printf("Cannot Determine
");
            return 0;        
        }
        else flag = max(flag, p);
        if(i != p) swap(A[i],A[p]);    
        for(int j = i + 1; j <= m; j++)
        if(A[j][i]) A[j]^=A[i];
    }
    ans[n] = A[n][n+1];
    for(int i = n - 1; i >= 1; i--)
    {
        ans[i] = A[i][n+1];
        for(int j = i + 1; j <= n; j++)
            ans[i] ^= ans[j] * A[i][j];    
    }
    printf("%d
",flag);
    for(int i = 1; i <= n; i++)
    {
        if(ans[i] == 0) printf("Earth
");
        if(ans[i] == 1) printf("?y7M#
");
    }
    return 0;
}