LibreOj 6000 搭配飞行员

传送门

分析:

一道简单的网络流模板题，也可以用匈牙利算法写。

代码:

#include <bits/stdc++.h>

using namespace std;

const int maxn = 1e5;

struct Edge
{
    int v , to;
    int next;
} edge[maxn];
int head[maxn] , cnt , n , m , from , to;
void add_edge(int from , int to , int v)
{
    edge[cnt].to = to;
    edge[cnt].v  = v;
    edge[cnt].next = head[from];
    head[from] = cnt++;
}

int level[maxn];
bool bfs()
{
    memset(level , 0 , sizeof level);
    level[from] = 1;

    queue<int> que;
    while(!que.empty()) que.pop();

    que.push(from);
    while(!que.empty())
    {
        int u = que.front();
        que.pop();
        for(int i=head[u]; i!=-1; i=edge[i].next)
        {
            if(!level[edge[i].to] && edge[i].v > 0)
            {
                level[edge[i].to] = level[u] + 1;
                que.push(edge[i].to);
            }
        }
    }
    return level[to];
}
int cur[maxn] , numm = 0;
int dfs(int u , int low)
{
    if(u == to)
    {
        return low;
    }
    int a;
    for(int &i=cur[u]; i!=-1; i=edge[i].next)
    {
        if(level[edge[i].to] == level[u] + 1 && edge[i].v > 0)
        {
            a = dfs(edge[i].to , min(low , edge[i].v));
            if(a)
            {
                edge[i].v   -= a;
                edge[i^1].v += a;
                return a;
            }
        }
    }
    return 0;
}
int total;
int solve()
{
    int sum = 0 , a;
    while(bfs())
    {
        memcpy(cur , head , sizeof head);
        while((a = dfs(from , 0x3f3f3f3f)))
            sum += a;
    }
    return sum; 
}
void init()
{
    memset(head , -1 , sizeof head);
    cnt = 0 , total = 0;
    from = 0 , to = m + n + 1;
}

int main()
{
    //freopen("data.in" , "r" , stdin);
    scanf("%d %d" , &n , &m);
    init();
    int a , b;
    while(~scanf("%d %d" , &a , &b))
    {
        add_edge(a , b , 1);
        add_edge(b , a , 0);
    }
    for(int i=1; i<=m; i++)
    {
        add_edge(from , i , 1);
        add_edge(i , from , 0);
    }
    for(int i=m+1; i<=n; i++)
    {
        add_edge(i , to , 1);
        add_edge(to , i , 0);
    }
    printf("%d\n" , solve());

    return 0;
}