HDU 4185 Oil Skimming（离散化 + 二分图匹配）

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <vector>
#include <queue>
#include <stack>
#include <cmath>
#include <algorithm>
#define LL long long
#define FOR(i, x, y) for(int i=x;i<=y;i++)
using namespace std;
const int MAXN = 600 + 10;
int G[MAXN][MAXN];
int vis[MAXN];
int match[MAXN];
int id[MAXN][MAXN];
int n, m;
char s[MAXN][MAXN];
int path(int u)
{
    for(int v=1;v<=m;v++)
    {
        if(G[u][v] && !vis[v])
        {
            vis[v] = 1;
            if(match[v] == -1 || path(match[v]))
            {
                match[v] = u;
                return 1;
            }
        }
    }
    return 0;
}
int main()
{
    int T, kcase = 1;
    scanf("%d", &T);
    while(T--)
    {
        int N;
        scanf("%d", &N);
        memset(id, 0, sizeof(id));
        int x = 0;
        for(int i=1;i<=N;i++)
        {
            scanf("%s", s[i] + 1);
            for(int j=1;j<=N;j++)
            {
                if(s[i][j] == '#')
                    id[i][j] = ++x;
            }
        }
        n = m = x;
        memset(G, 0, sizeof(G));
        FOR(i, 1, N)
        {
            FOR(j, 1, N)
            {
                if(s[i][j] == '#')
                {
                    if(i > 1 && s[i-1][j] == '#')
                        G[id[i-1][j]][id[i][j]] = 1;
                    if(i < N && s[i+1][j] == '#')
                        G[id[i+1][j]][id[i][j]] = 1;
                    if(j > 1 && s[i][j-1] == '#')
                        G[id[i][j-1]][id[i][j]] = 1;
                    if(j < N && s[i][j+1] == '#')
                        G[id[i][j+1]][id[i][j]] = 1;
                }
            }
        }
        int ans = 0;
        memset(match, -1, sizeof(match));
        for(int i=1;i<=n;i++)
        {
            memset(vis, 0, sizeof(vis));
            ans += path(i);
        }
        printf("Case %d: %d\n", kcase++, ans / 2);
    }
    return 0;
}