POJ2239 Selecting Courses（二分图最大匹配）

题目链接

N节课，每节课在一个星期中的某一节，求最多能选几节课

好吧，想了半天没想出来，最后看了题解是二分图最大匹配，好弱

建图： 每节课 与 时间有一条边

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
const int N = 300 + 5;
int vis[N], Left[N];
vector<int> g[N];
int n;
bool mach(int u)
{
    int Size = g[u].size();
    for (int i = 0; i < Size; i++)
    {
        int v = g[u][i];
        if (!vis[v])
        {
            vis[v] = 1;
            if (Left[v] == -1 || mach(Left[v]))
            {
                Left[v] = u;
                return true;
            }
        }
    }
    return false;
}
int main()
{
    while (scanf("%d", &n) != EOF)
    {
        int t, p, q;
        for (int i = 0; i <= n; i++)
            g[i].clear();
        for (int i = 1; i <= n; i++)
        {
            scanf("%d", &t);
            for (int j = 1; j <= t; j++)
            {
                scanf("%d%d", &p, &q);
                g[i].push_back(p * 12 + q); // 可以将每一节转化成一个整数
            }
        }
        memset(Left, -1, sizeof(Left));
        int ans = 0;
        for (int i = 1; i <= n; i++)
        {
            memset(vis, 0, sizeof(vis));
            if (mach(i))
                ans++;
        }
        printf("%d
", ans);
    }
    return 0;
}