枚举——POJ1753

#include<iostream>
#include<bitset>
#include<queue>

using namespace std;
queue<bitset<16>> state;		//record the state of each situation
bool flag[65536] = { false };	<span style="white-space:pre">	</span>//in case repeated search
int step[65536] ;

void Initialize()
{
cout << "Please input a 4*4 rectangle while 'b' represents 'black' "
<< "and 'w' represents 'white':\n";

char c;
int i = 0, j = 0;
bitset<16> temp;
for (i = 0; i < 4; i++)
{
for (j = 0; j < 4; j++)
{
cin >> c;
if ('b' == c)
temp.set(4 * i + j);
}
}
state.push(temp);
flag[temp.to_ulong()] = true;

}
bitset<16> Flip(bitset<16> piece, int i)
{

if (i % 4 != 0)			//not in the first column
piece.reset(i - 1);
if ((i + 1) % 4 != 0)	//not in the fourth column
piece.reset(i + 1);
if (i > 3)				//not in the first row
piece.reset(i - 4);
if (i < 12)				//not in the fourth row
piece.reset(i + 4);

return piece;
}
bool breadFirstSearch()
{
while (!state.empty())
{
bitset<16> firstState = state.front();
state.pop();							//queue.pop() do not return the value of the first item!
for (int i = 0; i < 16; i++)
{
bitset<16> temp = Flip(firstState, i);
if (firstState.none() || (firstState.count() == 16))
{
cout << step[firstState.to_ulong()];
return true;
}
else if(!flag[temp.to_ulong()])
{
state.push(temp);
flag[temp.to_ulong()] = true;
step[temp.to_ulong()] = step[firstState.to_ulong()] + 1;
}
}
}
return false;
}
int main()
{
Initialize();
if (!breadFirstSearch())
cout << "Impossible!";

return 0;
}