poj 3185 The Water Bowls 高斯消元枚举变元

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
int a[50][50], ans[50], x[50];
int n, l[50], free_x[50];
int gauss(int equ,int var)
{
    int i,j,k, max_r, col = 0, temp, free_index, num = 0;
    for(int i=0;i<=var;i++)
    {
        x[i]=0;
        free_x[i]=0;
    }
    for(k = 0;k < equ && col < var;k++,col++)
    {
        max_r=k;
        for(i=k+1;i<equ;i++)
        {
            if(abs(a[i][col])>abs(a[max_r][col])) max_r=i;
        }
        if(max_r!=k)
        {
            for(j=k;j<var+1;j++) swap(a[k][j],a[max_r][j]);
        }
        if(a[k][col]==0)
        {
            k--;
            free_x[num++]=col;
            continue;
        }
        for(i=k+1;i<equ;i++)
        {
            if(a[i][col]!=0)
            {
                for(j=col;j<var+1;j++)
                {
                    a[i][j] ^= a[k][j];
                }
            }
        }
    }
    for (i = k; i < equ; i++)
    {
        if (a[i][col] != 0) return -1;
    }
    int stat = 1<<(var-k);
    int res = inf;
    for(i=0;i<stat;i++)
    {
        int cnt=0;
        int index=i;
        for(j=0;j<var-k;j++)
        {
            x[free_x[j]]=(index&1);
            if(x[free_x[j]]) cnt++;
            index>>=1;
        }
        for(j=k-1;j>=0;j--)
        {
            int tmp=a[j][var];
            int t=0;
            while(a[j][t]==0)t++;
            for(int l=t+1;l<var;l++)
              if(a[j][l]) tmp^=x[l];
            x[t]=tmp;
            if(x[t])cnt++;
        }
        if(cnt<res)res=cnt;
    }
    return res;
}
int main()
{
    for(int i = 0; i<20; i++) {
        scanf("%d", &a[i][20]);
    }
    for(int i = 0; i<20; i++) {
        if(i) {
            a[i][i-1] = 1;
        }
        if(i!=19)
            a[i][i+1] = 1;
        a[i][i] = 1;
    }
    int ans = gauss(20, 20);
    cout<<ans<<endl;
    return 0;
}