poj1753

暴力dfs

#include <iostream>

#include <cstdio>

#include <cstring>

#include <cstdlib>

using namespace std;



bool map[4][4];

int ans = 100;



void init()

{

    int i, j;



    for (i = 0; i < 4; i++)

    {

        for (j = 0; j < 4; j++)

        {

            char ch;

            cin >> ch;

            if (ch == 'b')

                map[i][j] = true;

            else

                map[i][j] = false;

        }

        getchar();

    }

}



void operate(int x, int y)

{

    if (x < 0 || y < 0 || x > 3 || y > 3)

        return;

    map[x][y] = !map[x][y];

}



void turn(int pos)

{

    int x = pos / 4;

    int y = pos % 4;

    operate(x, y);

    operate(x + 1, y);

    operate(x, y + 1);

    operate(x - 1, y);

    operate(x, y - 1);

}



bool finished()

{

    int tot = 0;

    int i;

    for (i = 0; i < 16; i++)

        tot += map[i / 4][i % 4];

    return ((tot % 16) == 0);

}



void dfs(int pos, int step)

{

    if (finished())

    {

        if (ans > step)

            ans = step;

        return;

    }

    if (pos >= 16)

        return;

    dfs(pos + 1, step);

    turn(pos);

    dfs(pos + 1, step + 1);

    turn(pos);

}



int main()

{

    //freopen("D:\\t.txt", "r", stdin);

    init();

    dfs(0, 0);

    if (ans == 100)

        cout << "Impossible" << endl;

    else

        cout << ans << endl;

    return 0;

}

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