题目地址：HDU 3861
这题虽然是两个算法结合起来的。但是感觉挺没意思的。。结合的一点也不自然，，硬生生的揉在了一块。。。（出题者不要喷我QAQ。）
不过这题让我发现了我的二分匹配已经好长时间没用过了。。都快忘了。。正好在省赛之前又复习了一下。
代码如下：
#include <iostream>#include <string.h>#include <math.h>#include <queue>#include <algorithm>#include <stdlib.h>#include <map>#include <set>#include <stdio.h>using namespace std;#define LL __int64#define pi acos(-1.0)const int mod=1e9+7;const int INF=0x3f3f3f3f;const double eqs=1e-9;const int MAXN=5000+50;const int MAXM=100000+50;int head[MAXN], cnt, indx, top, ans;int low[MAXN], dfn[MAXN], belong[MAXN], instack[MAXN], stk[MAXN];struct node{int u, v, next;}edge[MAXM];void add(int u, int v){edge[cnt].v=v;edge[cnt].u=u;edge[cnt].next=head[u];head[u]=cnt++;}void tarjan(int u){low[u]=dfn[u]=++indx;instack[u]=1;stk[++top]=u;for(int i=head[u];i!=-1;i=edge[i].next){int v=edge[i].v;if(!dfn[v]){tarjan(v);low[u]=min(low[u],low[v]);}else if(instack[v]){low[u]=min(low[u],dfn[v]);}}if(low[u]==dfn[u]){ans++;while(1){int v=stk[top–];instack[v]=0;belong[v]=ans;if(u==v) break;}}}void init(){memset(head,-1,sizeof(head));memset(dfn,0,sizeof(dfn));memset(instack,0,sizeof(instack));cnt=indx=top=ans=0;}int head1[MAXN], cnt1, vis[MAXN], link[MAXN];struct N{int u, v, next;}edge1[MAXM*2];void add1(int u, int v){edge1[cnt1].v=v;edge1[cnt1].next=head1[u];head1[u]=cnt1++;}int dfs(int u){for(int i=head1[u];i!=-1;i=edge1[i].next){int v=edge1[i].v;if(!vis[v]){vis[v]=1;if(link[v]==-1||dfs(link[v])){link[v]=u;return 1;}}}return 0;}void hungary(){memset(link,-1,sizeof(link));int i, sum=0;for(i=1;i<=ans;i++){memset(vis,0,sizeof(vis));sum+=dfs(i);}printf("%d\n",ans-sum);}int main(){int t, n, m, u, v, i;scanf("%d",&t);while(t–){scanf("%d%d",&n,&m);init();while(m–){scanf("%d%d",&u,&v);add(u,v);}for(i=1;i<=n;i++){if(!dfn[i]) tarjan(i);}memset(head1,-1,sizeof(head1));cnt1=0;for(i=0;i<cnt;i++){u=belong[edge[i].u];v=belong[edge[i].v];if(u!=v){add1(u,v);}}hungary();}return 0;}
，微笑的去寻找一个不可能出现的你。
