【luogu P2071 座位安排】 题解

题目链接：https://www.luogu.org/problemnew/show/P2071#sub

邻接表 + 匈牙利

把之前的邻接矩阵匈牙利变成邻接表

要不然存不下...

code：

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
inline int read()
{
    int ret=0;
    char c=getchar();
    while (c<'0' || c>'9') c=getchar();
    while (c>='0' && c<='9'){
        ret=((ret<<3)+(ret<<1))+c-'0';
        c=getchar();
    }
    return ret;
}
const int maxn = 4010;
int n, ans, cnt;
int link[maxn], head[maxn];
bool vis[maxn];
struct edge{
    int v,next;
}e[maxn<<2];
void add(int u, int v)
{
    e[++cnt].v = v;
    e[cnt].next = head[u];
    head[u] = cnt;
}
bool dfs(int u)
{
    int v = head[u];
    for(int i = v; i != 0; i = e[i].next)
    {
        if(!vis[e[i].v])
        {
            vis[e[i].v] = 1;
            if(!link[e[i].v] || dfs(link[e[i].v])) 
            {
                link[e[i].v] = u;
                return 1;
            }
        }    
    }
    return 0;
}
int main()
{
    int u,v;
    n = read();
    for(int i = 1; i <= n*2; i++)
    {
        u = read(); v = read();
        add(i,u);
        add(i,u+n);
        add(i,v);
        add(i,v+n);
    }
    for(int i = 1; i <= n*2; i++)
    {
        memset(vis,0,sizeof(vis));
        if(dfs(i)) ans++;
    }
    printf("%d",ans);
    return 0; 
}