HDU - 2444 The Accomodation of Students(二分圖匹配)

HDU - 2444 

題意：有兩兩認識的一些同學，但是a認識b，b認識c，不代表a認識c，求這個關係能否構成二分圖，以及最大匹配

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const int maxe = 4e4 + 50,maxn = 250;
struct node
{
    int to,next;
    node(){}
    node(int a,int b){to = a ; next = b;}
}edge[maxe << 1];
int h[maxn],col[maxn],belong[maxn],used[maxn];

int edgenum = 0;
void init()
{
    edgenum = 0;
    for(int i = 0; i < maxn; i++)   col[i] = h[i] = -1,belong[i] = used[i] = 0;
}
void add(int t,int f)
{
    edge[edgenum] = node(t,h[f]);
    h[f] = edgenum++;
}
bool colour(int u)
{
    int now = !col[u];
    for(int i = h[u]; ~i; i = edge[i].next)
    {
        int v = edge[i].to;
        if(col[v] == -1)
        {
            col[v] = now;
            if(colour(v) == 0) return false;
        }
        else if(col[v] == col[u])
            return false;
    }
    return true;
}
bool Find(int u)
{
    for(int i = h[u]; ~i ; i = edge[i].next)
    {
        int v = edge[i].to;
        if(used[v] == 1) continue;
        used[v] = 1;

        if(!belong[v] || Find(belong[v]))
        {
            belong[v] = u;
            return true;
        }
    }
    return false;
}
int main()
{
    int n,m;
    while(~scanf("%d%d",&n,&m))
    {
        int a,b;
        init();
        for(int i = 0; i < m ; i++)
        {
            scanf("%d%d",&a,&b);
            add(a,b);   add(b,a);
        }
        int flag = 0;
        for(int u = 1; u <= n ; u++)
        {
            if(col[u] != -1) continue;
            col[u] = 1;
            if(colour(u) == 0) {flag = 1;break;}
        }
        if(flag) printf("No\n");
        else
        {
            int ans = 0;
            for(int i = 1; i <= n; i++)
            {
                memset(used,0,sizeof(used));
                if(col[i] == 1) continue;
                if(Find(i)) ans++;
            }
            printf("%d\n",ans);
        }
    }
    return 0;
}