Fliptile

Time Limit: 2000MS		Memory Limit: 65536K
Total Submissions: 19730		Accepted: 7118

Farmer John knows that an intellectually satisfied cow is a happy cow who will give more milk. He has arranged a brainy activity for cows in which they manipulate an M × N grid (1 ≤ M ≤ 15; 1 ≤ N ≤ 15) of square tiles, each of which is colored black on one side and white on the other side.

As one would guess, when a single white tile is flipped, it changes to black; when a single black tile is flipped, it changes to white. The cows are rewarded when they flip the tiles so that each tile has the white side face up. However, the cows have rather large hooves and when they try to flip a certain tile, they also flip all the adjacent tiles (tiles that share a full edge with the flipped tile). Since the flips are tiring, the cows want to minimize the number of flips they have to make.

Help the cows determine the minimum number of flips required, and the locations to flip to achieve that minimum. If there are multiple ways to achieve the task with the minimum amount of flips, return the one with the least lexicographical ordering in the output when considered as a string. If the task is impossible, print one line with the word "IMPOSSIBLE".

Line 1: Two space-separated integers: M and N 
Lines 2..M+1: Line i+1 describes the colors (left to right) of row i of the grid with N space-separated integers which are 1 for black and 0 for white

Lines 1..M: Each line contains N space-separated integers, each specifying how many times to flip that particular location.

4 4

1 0 0 1

0 1 1 0

0 1 1 0

1 0 0 1

0 0 0 0

1 0 0 1

1 0 0 1

0 0 0 0

思路：
因为求解的是最小按键次数，如果将所有都遍历的话，时间复杂度为 2^(N*M)太大了，因为开关按下，上下左右和它自己都会变化，所以，让第一行出现2^m次不同的情况，用二进制表示

#include <stdio.h>

#include <cstring>

#include <algorithm>

#include <string.h>

#include <math.h>

#include <stdlib.h>

#include <iostream>

using namespace std;

int map[][],mm[][];

int a[][],A[][];

int d[][] = {,,,,-,,,,,-};

int get_s(int x,  int y){

    if(map[x][y]==) return ;

    else return ;

}

int main(){

    int n,m;

    cin>>n>>m;

    memset(map,,sizeof(map));

    for(int i=;i<=n;i++){

        for(int j=;j<=m;j++){

            cin>>map[i][j];

        }

    }

    memcpy(mm,map,sizeof(map));

    int minn = 1e9;

    for( int i = ; i < <<m; i++ ) {

        int count=,flag = ;

        memset(a,,sizeof(a));

        memcpy(map,mm,sizeof(mm));

        //第一行解决 将 i 转化为 二进制

        for(int j=;j<=m;j++){

            a[][j] = (i>>(j-))&;

            if( a[][j] == ){

                count++;

                map[][j]   = get_s(,j);

                map[][j-] = get_s(,j-);

                map[][j+] = get_s(,j+);

                map[][j]   = get_s(,j);

            }

        } 

        for( int j = ; j < n; j++ ) {

            for( int k = ; k <= m; k++ ) {

                if( map[j][k] ==  ) {

                    a[j+][k] = ;

                    int dx = j+, dy = k, tx, ty;

                    count++;

                    for( int z = ; z < ; z++ ) {

                        tx = dx + d[z][];

                        ty = dy + d[z][];

//                        cout<<tx<<" "<<ty<<endl;

                        map[tx][ty] = get_s(tx,ty);

                    }

//                    cout<<map[j][k]<<"  "<<" j = "<<j<<" k = "<<k<<endl;

                }

            }

        }

        for( int j = ; j <= m; j++ ) {

            if(map[n][j]==) flag = ;

        }

        if( flag ) continue;

        else {

            if( count < minn ) {

                minn = count;

                memcpy(A,a,sizeof(a));

            }

        }

    }

    if(minn == 1e9) printf("IMPOSSIBLE\n");

    else{

        for(int i=;i<=n;i++)

            for(int j=;j<=m;j++)

                printf("%d%c",A[i][j],j==m?'\n':' ');

    }

    return ;

}