Hdu1151 air raid (directed graph least path overwrite)

Question:

Directed Graph with m edges at N points

It means to ask the minimum coverage

Ideas:

A directed graph is used to create a unidirectional edge, and Hungary calculates the maximum matching number.

Use the n-Max match.

/* ***********************************************Author        :devilCreated Time  :2016/5/17 11:55:14************************************************ */#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <set>#include <map>#include <string>#include <cmath>#include <stdlib.h>using namespace std;const int N=125;int link[N];bool vis[N];vector<int>eg[N];bool dfs(int u){    for(int i=0;i<eg[u].size();i++)    {        int v=eg[u][i];        if(!vis[v])        {            vis[v]=1;            if(link[v]==-1||dfs(link[v]))            {                link[v]=u;                return 1;            }        }    }    return 0;}int main(){    //freopen("in.txt","r",stdin);    int t,n,m,x,y;    scanf("%d",&t);    while(t--)    {        scanf("%d%d",&n,&m);        memset(link,-1,sizeof(link));        for(int i=1;i<=n;i++)            eg[i].clear();        while(m--)        {            scanf("%d%d",&x,&y);            eg[x].push_back(y);        }        int ans=0;        for(int i=1;i<=n;i++)        {            memset(vis,0,sizeof(vis));            ans+=dfs(i);        }        printf("%d\n",n-ans);    }    return 0;}

 

Hdu1151 air raid (directed graph least path overwrite)