POJ_1753——Flip Game（枚举）

 #include<iostream>
using namespace std;
 
const int N = 4;
bool map[N][N],flag;
int step;
 
//判断全白或全黑
bool judge(){
    int i,j;
    for( i = 0; i < N; i++ )
        for( j = 0; j < N; j++ ){
            if( map[i][j] != **map )
                return false;
           }
    return true;
}
 
//翻转棋子
void flip(int i, int j){
    map[i][j] = !map[i][j];
    if( i > 0 )
        map[i-1][j] = !map[i-1][j];
    if( i < 3 )
        map[i+1][j] = !map[i+1][j];
    if( j > 0 )
        map[i][j-1] = !map[i][j-1];
    if( j < 3 )
        map[i][j+1] = !map[i][j+1];
 }
 
 
void dfs(int i, int j, int dp){
 
    if( dp == step ){
        flag = judge();
        return;
    }
 
    if( flag || i == N )
        return;
 
    flip(i,j);//翻转
    if( j < 3 )
        dfs(i,j+1,dp+1);
    else
        dfs(i+1,0,dp+1);
    flip(i,j);//还原
 
    if( j < 3 )
        dfs(i,j+1,dp);
    else
        dfs(i+1,0,dp);
}
 
int main(void){
    int i,j;
    char c;
 
    for( i = 0; i < N; i++ )
        for( j = 0; j < N; j++ ){
            cin >> c;
            if( c == ‘b‘ )
                map[i][j] = 1;
        }
 
    //枚举翻转次数
    for( step = 0; step <= 16; step++ ){
        dfs(0,0,0);
        if( flag ){
            cout << step <<endl;
            return 0;
        }
    }
 
    cout << "Impossible" <<endl;
    return 0;
}