poj1753枚举

Flip Game

Description

Flip game is played on a rectangular 4x4 field with two-sided pieces placed on each of its 16 squares. One side of each piece is white and the other one is black and each piece is lying either it‘s black or white side up. Each round you flip 3 to 5 pieces, thus changing the color of their upper side from black to white and vice versa. The pieces to be flipped are chosen every round according to the following rules:

1. Choose any one of the 16 pieces.
2. Flip the chosen piece and also all adjacent pieces to the
   left, to the right, to the top, and to the bottom of the chosen piece
   (if there are any).

Consider the following position as an example:

bwbw

wwww

bbwb

bwwb

Here "b" denotes pieces lying their black side up and "w" denotes
pieces lying their white side up. If we choose to flip the 1st piece
from the 3rd row (this choice is shown at the picture), then the field
will become:

bwbw

bwww

wwwb

wwwb

The goal of the game is to flip either all pieces white side up or
all pieces black side up. You are to write a program that will search
for the minimum number of rounds needed to achieve this goal.

Input

The input consists of 4 lines with 4 characters "w" or "b" each that denote game field position.

Output

Write
to the output file a single integer number - the minimum number of
rounds needed to achieve the goal of the game from the given position.
If the goal is initially achieved, then write 0. If it‘s impossible to
achieve the goal, then write the word "Impossible" (without quotes).

Sample Input

bwwb
bbwb
bwwb
bwww

Sample Output

4

Source

解析

真是醉了，双重dfs，如果对dfs不是很了解的同学就放弃这道题吧，想了4个小时才想通，脑细胞都快没了，

其实就是step从0枚举到16，之后dfs结构中主要是对每一种可能进行位移式的枚举，一部一部向后推得枚举

附代码

ps：其实本人代码与网上的代码差不多，

本人也是参考网上代码才解决的这道问题

如过有谁不懂可以Q我，1097944404

#include<iostream>
#include<string.h>
#include<stdio.h>
#include<algorithm>
using namespace std;
int map[5][5],step,flag;
int judge(){
     for(int i=0;i<4;i++){
        for(int j=0;j<4;j++){
             if(map[i][j]!=map[0][0])
                return 0;
        }
     }
     return 1;
}
void update(int x,int y){
    map[x][y]^=1;
      if(x>0)
          map[x-1][y]^=1;
      if(x<3)
         map[x+1][y]^=1;
         if(y>0)
         map[x][y-1]^=1;
         if(y<3)
         map[x][y+1]^=1;
}

void dfs(int x,int y,int step1){
    if(step1==step){
         flag=judge();
         return ;
    }
    if(flag||x==4)
         return;
       update(x,y);
       if(y<3)
         dfs(x,y+1,step1+1);
         else
         dfs(x+1,0,step1+1);
         update(x,y);
         if(y<3)
         dfs(x,y+1,step1);
         else
         dfs(x+1,0,step1);

}
int main(){
       char z;
       for(int i=0;i<4;i++){
          for(int j=0;j<4;j++){
             scanf("%c",&z);
             if(z==‘b‘)
                  map[i][j]=0;
                  else
                  map[i][j]=1;
          }
          getchar();
       }
            flag=0;
       for( step=0;step<=16;step++){
           dfs(0,0,0);
           if(flag)
             break;
       }
       if(flag)
           printf("%d\n",step);
       else
       printf("Impossible\n");

return 0;
}