hdu 1045 Fire Net(最小覆盖点+构图（缩点））

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
#define N 310

using namespace std;

char maps[N][N];
int G[N][N], vis[N], used[N];
int n, x, y, a[N][N], b[N][N];

bool Find(int u)
{
    int i;
    for(i = 1 ; i <= y ; i++)
    {
        if(!vis[i] && G[u][i])
        {
            vis[i] = 1;
            if(!used[i] || Find(used[i]))
            {
                used[i] = u;
                return true;
            }
        }
    }
    return false;
}

void Build()
{
    int i, j;
    x = y = 0;
    memset(a, 0, sizeof(a));
    memset(b, 0, sizeof(b));
    for(i = 1 ; i <= n ; i++)
    {
        for(j = 1 ; j <= n ; j++)
        {
            if(maps[i][j] == ‘.‘)
            {
                if(maps[i][j - 1] == ‘.‘)
                    a[i][j] = a[i][j - 1];
                else
                    a[i][j] = ++x;
            }
        }
    }
    for(i = 1 ; i <= n ; i++)
    {
        for(j = 1 ; j <= n ; j++)
        {
            if(maps[i][j] == ‘.‘)
            {
                if(maps[i - 1][j] == ‘.‘)
                    b[i][j] = b[i - 1][j];
                else
                    b[i][j] = ++y;
                G[a[i][j]][b[i][j]] = 1;
            }
        }
    }

}

int main()
{
    int i, j, ans;
    while(scanf("%d", &n), n)
    {
        ans = 0;
        memset(G, 0, sizeof(G));
        for(i = 1 ; i <= n ; i++)
        {
            getchar();
            for(j = 1 ; j <= n ; j++)
                 scanf("%c", &maps[i][j]);
        }
        Build();
        memset(used, 0, sizeof(used));
        for(i = 1 ; i <= x ; i++)
        {
            memset(vis, 0, sizeof(vis));
            if(Find(i))
                ans++;
        }
        printf("%d\n", ans);
    }
    return 0;
}