BZOJ1923: [Sdoi2010]外星千足虫

题目：http://www.lydsy.com/JudgeOnline/problem.php?id=1923

高斯消元。

（bitset好优越啊。。

#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<bitset>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define down(i,l,r) for (int i=l;i>=r;i--)
#define clr(x,y) memset(x,y,sizeof(x))
#define maxn 2005
using namespace std;
bitset<1005> a[2005];
int n,m,l,r,ans;
char s[maxn];
int read(){
    int x=0,f=1; char ch=getchar();
    while (!isdigit(ch)) {if (ch==‘-‘) f=-1; ch=getchar();}
    while (isdigit(ch)) {x=x*10+ch-‘0‘; ch=getchar();}
    return x*f;
}
void gs(){
    rep(i,1,n){
        int now=i;
        while (now<=m&&a[now][i]==0) now++;
        ans=max(ans,now);
        if (now==m+1) {ans=-1; return;}
        swap(a[now],a[i]);
        rep(j,1,m) if (i!=j&&a[j][i]) a[j]^=a[i];
    }
}
int main(){
    n=read(); m=read();
    rep(i,1,m){
        scanf("%s",s); a[i][n+1]=read();
        rep(j,1,n) a[i][j]=s[j-1]-‘0‘;
    }
    gs();
    if (ans==-1) puts("Cannot Determine");
    else {
        printf("%d\n",ans);
        rep(i,1,n) if (a[i][n+1]) puts("?y7M#");
        else puts("Earth");
    }
    return 0;
}