[acm 1002] 浙大 Fire Net

#include <iostream>
#include <cstdlib>
#include <cmath>

#include <list>

#define OPEN 1
#define CASTLE 2
#define BLOCK 3
#define WALL 4

// summary: 用贪心原理找到一个影响地图最小的城堡的位置
// param in: map[] 输入的地图. n 地图大小.
// param out: min_x,min_y  得出的放置的城堡的x,y坐标
// return: true 找到了合适的位置. false 没有可以放置城堡的地方了
#define MAX_POINT 10000 // 哨兵数
bool FindMinInfluencePosition(int map[][4], int n, int &min_x, int &min_y)
{
    int min_point = MAX_POINT; // 赋哨兵值
    min_x = min_y = 0;

    for (int y = 0; y < n; y++)
    {
        for (int x = 0; x < n; x++)
        {
            if ( map[y][x] == OPEN)
            {
                int curr_point = 1;

                // 向上
                for (int j = y - 1; j >= 0 && map[j][x] != WALL; j--)
                {
                    if ( map[j][x] == OPEN)
                        curr_point++;
                }

                // 向下
                for (int j = y + 1; j < n && map[j][x] != WALL; j++)
                {
                    if ( map[j][x] == OPEN)
                        curr_point++;
                }

                // 向左
                for (int j = x - 1; j >= 0 && map[y][j] != WALL; j--)
                {
                    if ( map[y][j] == OPEN)
                        curr_point++;
                }

                // 向右
                for (int j = x + 1; j < n && map[y][j] != WALL; j++)
                {
                    if ( map[y][j] == OPEN)
                        curr_point++;
                }

                if (curr_point < min_point)
                {
                    min_point = curr_point;
                    min_x = x;
                    min_y = y;
                }
            }
        }
    }

    // 检测是否放置了城堡
    if (min_point != MAX_POINT)
        return true;
    else
        return false;

}

// summary: 根据位置放置城堡，在地图上标记出来
// param in: map[] 输入的地图. n 地图大小. x, y 放置的城堡的位置
void PlaceCastle(int map[][4], int n, int x, int y)
{
    map[y][x] = CASTLE;

    // 向上
    for (int j = y - 1; j >= 0 && map[j][x] != WALL; j--)
    {
        map[j][x] = BLOCK;
    }

    // 向下
    for (int j = y + 1; j < n && map[j][x] != WALL; j++)
    {
        map[j][x] = BLOCK;
    }

    // 向左
    for (int j = x - 1; j >= 0 && map[y][j] != WALL; j--)
    {
        map[y][j] = BLOCK;
    }

    // 向右
    for (int j = x + 1; j < n && map[y][j] != WALL; j++)
    {
        map[y][j] = BLOCK;
    }
}


int main ()
{
    int map[4][4];
    std::list<int> answer;
    int n;
    char c;

    // 读取数据
    std::cin>>n;
    while (n != 0)
    {
        // 读取地图数据
        for (int y = 0; y < n; y++)
        {
            for (int x = 0; x < n; x++)
            {
                std::cin>>c;
                if (c == ‘.‘)
                    map[y][x] = OPEN;
                else
                    map[y][x] = WALL;
            }
        }

        // 处理地图
        int castle_number = 0;
        int min_x, min_y;
        while (FindMinInfluencePosition(map, n, min_x, min_y) == true )
        {
            castle_number++;
            PlaceCastle(map, n, min_x, min_y);
        }

        // 记录数据
        answer.push_back(castle_number);

        // 输入下一个数
        std::cin>>n;
    }

    // 输出数目
    for (std::list<int>::iterator it=answer.begin() ; it != answer.end(); ++it)
        std::cout <<*it<<"\n";

    return 0;
}