Luogu P1764翻转游戏

我代码能力可能有一定的了，要不然不能一遍写出来吧。。

要注意无解的处理！

#include<iostream>
#include<cstdio>

using namespace std;

int a[20][20];
int n,ans = -1,k,cnt0;
char ch;

void print(){
    cout << endl;
    for(int i = 1;i <= n;i++){
        for(int j = 1;j <= n;j++)cout << a[i][j];
        cout << endl;
    }
    cout << endl;
}

void touch(int x,int y){
    a[x-1][y] ^= 1;
    a[x][y-1] ^= 1;
    a[x][y] ^= 1;
    a[x][y+1] ^= 1;
    a[x+1][y] ^= 1;
}

void work0(){
    for(int i = 1;i <= n;i++)
        if((k>>(i-1))&1)a[0][i] = 1;
        else a[0][i] = 0;
}

void work1(int cur,int cnt){//print();
    if(cur == n+1){
        for(int i = 1;i <= n;i++)if(!a[n][i])return;
        if(ans == -1||ans > cnt)ans = cnt;
        return;
    }
    int v = 0;
    for(int i = 1;i <= n;i++)if(!a[cur-1][i]){
        cnt++;
        touch(cur,i);
        v |= 1<<(i-1);
    }
    work1(cur+1,cnt);
    for(int i = 1;i <= n;i++)if((v>>(i-1))&1)touch(cur,i);
}

void work2(int cur,int cnt){//print();
    if(cur == n+1){
        for(int i = 1;i <= n;i++)if(a[n][i])return;
        if(ans == -1||ans > cnt)ans = cnt;
        return;
    }
    int v = 0;
    for(int i = 1;i <= n;i++)if(a[cur-1][i]){
        cnt++;
        touch(cur,i);
        v |= 1<<(i-1);
    }
    work2(cur+1,cnt);
    for(int i = 1;i <= n;i++)if((v>>(i-1))&1)touch(cur,i);
}

int main(){
    cin >> n;
    for(int i = 1;i <= n;i++)for(int j = 1;j <= n;j++){
        cin >> ch;
        if(ch == 'b')a[i][j] = 1;
        else a[i][j] = 0;
    }    
    for(k = 0;k < 1<<n;k++)work0(),work1(1,0),work2(1,0);
    if(ans != -1)cout << ans;
    else cout << "Impossible";
return 0;
}