poj1753（枚举）题解

poj1753

题目

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:
Choose any one of the 16 pieces.
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

题目意思

要求：输入一串4行4列的字符串（只包函b和w），将这字符串改为只包函一种字符；
改变规则：每改变一个点，将这个点和这个点的四个方向（上，下，左，右）上的点改变；
改变方式：b==>w，w==>b;

解题思路

枚举每一种情况；每一种情况都要判断是否满足题目要求；如果有满足要求的，就找出满足要求并且改变点最少的那一个情况；每一种情况都不满足则输出“Impossible”；

代码

#include<cstdio>
#include <iostream>
#include<cmath>
using namespace std;
char a[5][5];
bool all=false;
int mm=100