poj 1753（枚举）

#include<iostream>
using namespace std;
int d[5][5];
char c[5][5];
int mm = 65536;
bool all = false;
void change(int i,int j){
    d[i][j] = 1-d[i][j];
    if(i>1)d[i-1][j] = 1-d[i-1][j];
    if(i<4)d[i+1][j] = 1-d[i+1][j];
    if(j>1)d[i][j-1] = 1-d[i][j-1];
    if(j<4)d[i][j+1] = 1-d[i][j+1]; 
}
bool test(){
    int tmp = d[1][1];
    for(int i=1;i<=4;i++){
        for(int j=1;j<=4;j++){
            if(tmp!=d[i][j])return false;
        }
    }
    return true;
}
void meiju(int n,int m,int num){
    for(int i=1;i<=4;i++){
        for(int j=1;j<=4;j++){
            if(i<n||(i==n&&j<=m))
                continue;
            change(i,j);
            if(test()&&num<mm){
                mm = num;
                all = true;
            }
            meiju(i,j,num+1);
            change(i,j);
        }
    }
}
int main(){
    for(int i=1;i<=4;i++){
        for(int j=1;j<=4;j++){
            cin>>c[i][j];
            if(c[i][j]=='w')d[i][j] = 1;
            else            d[i][j] = 0;
        }
        getchar();
    }
    if(test()){
        cout<<0<<endl;return 0;
    }
    meiju(0,0,1);
    if(all){
        cout<<mm<<endl;
    }
    else{
        cout<<"Impossible"<<endl;
    }
    return 0;
}