bzoj 1923: [Sdoi2010]外星千足虫

题目链接

bzoj 1923: [Sdoi2010]外星千足虫

题解

高斯消元解xor方程

代码

#include<cstdio>
#include<bitset>
#include<cstring>
#include<algorithm>
using std::max;
using std::min;
using std::bitset;

inline int  read() {
    int x = 0,f = 1;
    char c = getchar();
    while(c < '0'||c > '9'){if(c=='-')f = -1;c = getchar();}
    while(c <= '9'&&c >= '0') x = x*10 + c-'0',c = getchar();
    return x * f;
}
const int maxn = 1007;
bitset<maxn>a[maxn*2];
int n,m,ans;
char s[maxn];

void Guass() {
    int now = 1;
    for(int i = 1;i <= n;++ i) {
        int j = now;
        while(j <= m&&!a[j][i]) j ++;
        if(j == m + 1) {ans = -1;break;}
        else ans = max(ans,j);
        swap(a[now],a[j]);
        for(int k = 1;k <= m;++ k) 
            if(k != now&&a[k][i]) a[k] ^= a[now];
        now++;
    }
} 
int main() {
    n = read(),m = read();
    for(int X,i = 1;i <= m;++ i) {
        scanf("%s",s + 1);
        for(int j = 1;j <= n;++ j) a[i][j]=s[j] - '0';
        a[i][n+1] = read();
    }
    Guass();
    if(ans == -1) { puts("Cannot Determine"); return 0;}
    printf("%d\n",ans);
    for(int i = 1;i <= n;++ i) {
        if(a[i][n + 1]) puts("?y7M#");
        else puts("Earth");
    }
    return 0;
}