SPOJ4206Fast Maximum Matching(hopcroft-karp)

题目请戳这里

题目大意：裸的二分匹配。

题目分析：数据比较强，用来测模版的。这题用hungry跑着会比较吃力，所以用hopcroft-karp算法。这个算法较hungry高效是因为每次bfs找到一个增广路集，然后用dfs进行多路增广，同时找多条增广路，从而效率大增。其实怎么看hk算法都是个没有边权的dinic啊。

参照着wikipedia 敲了一个hk，效率貌似不高啊。。。

详情请见代码：

 

#include <iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int N = 50001;
const int M = 150001;
const int inf = 0x3f3f3f3f;

int head[N];
struct node
{
    int to,next;
}g[M];
int m,n,p,num;
int matchx[N],matchy[N],que[N],dis[N];
void build(int s,int e)
{
    g[num].to = e;
    g[num].next = head[s];
    head[s] = num ++;
}
bool bfs()
{
    int i,j;
    int front,rear;
    front = rear = 0;
    for(i = 1;i <= n;i ++)
    {
        if(!matchx[i])
        {
            dis[i] = 0;
            que[rear ++] = i;
        }
        else
            dis[i] = inf;
    }
    dis[0] = inf;
    while(front != rear)
    {
        int u = que[front ++];
        if(front == N)
            front = 0;
        for(i = head[u];~i;i = g[i].next)
        {
            int v = g[i].to;
            if(dis[matchy[v]] == inf)
            {
                dis[matchy[v]] = dis[u] + 1;
                que[rear ++] = matchy[v];
                if(rear == N)
                    rear = 0;
            }
        }
    }
    return dis[0] != inf;
}
bool dfs(int u)
{
    int i,v;
    for(i = head[u];~i;i = g[i].next)
    {
        v = g[i].to;
        if(dis[matchy[v]] == dis[u] + 1)
            if(matchy[v] == 0 || dfs(matchy[v]))
            {
                matchx[u] = v;
                matchy[v] = u;
                return true;
            }
    }
    dis[u] = inf;
    return false;
}

void Hopcroft_Karp()
{
    memset(matchx,0,sizeof(matchx));
    memset(matchy,0,sizeof(matchy));
    int ans = 0;
    while(bfs())
    {
        for(int i = 1;i <= n;i ++)
            if(!matchx[i])
                if(dfs(i))
                    ans ++;
    }
    printf("%d\n",ans);
}
int main()
{
    int a,b;
    while(scanf("%d",&n) != EOF)
    {
        memset(head,-1,sizeof(head));
        num = 1;
        scanf("%d%d",&m,&p);
        while(p --)
        {
            scanf("%d%d",&a,&b);
            build(a,b);
        }
        Hopcroft_Karp();
    }
    return 0;
}