poj1753

http://acm.pku.edu.cn/JudgeOnline/problem?id=1753

就是普通的广搜，状态存储用一位表示一个格是黑还是白（0黑1白），听大牛说可以通过异或运算来进行状态转移，不过我不会，就直接进行加减运算了。

 

#include<iostream>
#include<stdlib.h>
using namespace std;
char board[4][4];
int hash[65536],state,temp_state,temp_i,temp_j;
int dx[4] = {0,0,1,-1},dy[4] = {1,-1,0,0},queue_start,queue_end,result = 0,result_sum;
int queue[100000],queue_sum[100000];
int main()
{
int i,j,k,sum;
queue_start = 0;
queue_end = 0;
memset(hash,0,sizeof(hash));
memset(queue_sum,0,sizeof(queue_sum));
state = 0;
for (i = 0;i < 4;i++)
for (j = 0;j < 4;j++)
{
cin>>board[i][j];
if (board[i][j] == 'b')
{
state += 1<<(i*4+j);
}
}
queue[queue_end++] = state;
hash[state] = 1;
while(queue_start < queue_end && !result)
{
state = queue[queue_start++];
temp_state = state;
sum = 0;
for (i = 0;i < 16;i++)
{
if (state&(1<<i)) sum++;
}
if (sum == 0 || sum == 16)
{
result = 1;
result_sum = queue_sum[queue_start-1];
}
for (i = 0;i < 4;i++)
for (j = 0;j < 4;j++)
{
temp_state = state;
temp_i = i;
temp_j = j;
if (state&(1<<(i*4+j)))
temp_state -= 1<<(i*4+j);
else
temp_state += 1<<(i*4+j);
for (k = 0;k <4;k++)
{
temp_i = i + dx[k];
temp_j = j + dy[k];
if (temp_i >=0 && temp_i < 4 && temp_j >=0 && temp_j < 4)
{
if (temp_state&(1<<(temp_i*4+temp_j)))
{
temp_state -= 1<<(temp_i * 4 + temp_j);
}
else
{
temp_state += 1<<(temp_i * 4 + temp_j);
}
}
}
if (!hash[temp_state])
{
hash[temp_state] = 1;
queue[queue_end] = temp_state;
queue_sum[queue_end] = queue_sum[queue_start-1] + 1;
queue_end++;
}
}
}
if (result)
cout<<result_sum<<endl;
else
cout<<"Impossible"<<endl;
system("Pause");
return 0;
}