Fliptile

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".

Input

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

Output

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

Sample Input

4 41 0 0 10 1 1 00 1 1 01 0 0 1

Sample Output

0 0 0 01 0 0 11 0 0 10 0 0 0

   枚举第一行的翻转所有翻转情况然后逐行向下更新，如果上一行是1的话，那么下面一行肯定要翻转，因为只有下面一行能影响上面一行。最后判断一下，最后一行是不是都是0，如果都是，则维护最小的翻转次数。

#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <algorithm>#include <queue>using namespace std;const int maxn = 25;const int INF = 0x3f3f3f3f;int n,m,res;int Map[maxn][maxn],vist[maxn][maxn];int temp[maxn][maxn],ans[maxn][maxn],tmp[maxn][maxn];int dx[5] = {0,0,0,1,-1};int dy[5] = {0,1,-1,0,0};void filp(int x,int y){    int nx,ny;    tmp[x][y] = 1;    for(int i = 0; i < 5; i++){        nx = x+dx[i];        ny = y+dy[i];        temp[nx][ny] = !temp[nx][ny];    }}bool judge(){    for(int i = 1; i <= m; i++)        if(temp[n][i])            return false;    return true;}void solve(int x){    memcpy(temp,Map,sizeof(Map));    memset(tmp,0,sizeof(tmp));    int cnt = 0;    for(int i = 0; i < m; i++){        if((x>>i) & 1){            filp(1,i+1);            cnt++;        }    }    for(int i = 2; i <= n; i++){        for(int j = 1; j <= m; j++){            if(temp[i-1][j] == 1){                filp(i,j);                cnt++;            }        }    }    if(judge() && cnt < res){        res = cnt;        memcpy(ans,tmp,sizeof(tmp));    }}int main(){    scanf("%d %d",&n,&m);    for(int i = 1; i <= n; i++)        for(int j = 1; j <= m; j++)            scanf("%d",&Map[i][j]);    res = INF;    int End = 1<<m;    for(int i = 0; i < End; i++)        solve(i);    if(res == INF)        puts("IMPOSSIBLE");    else{        for(int i = 1; i <= n; i++){            for(int j = 1; j <= m; j++){                if(j == m)                    printf("%d\n",ans[i][j]);                else                    printf("%d ",ans[i][j]);            }        }    }    return 0;}