Hdu oj 1350 taxi cab Scheme [minimum path Overwrite for Bipartite Graph Matching]

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Question :......

Idea: The minimum path coverage for binary matching. In a directed graph without loops, find the minimum path to overwrite all nodes, and each node can only overwrite once.

Overwrite all vertices of directed acyclic graph (DAG) g with a few non-Intersecting simple paths.
To solve this problem, you can create a bipartite graph model. Split all vertex I into two: I in the x node set and I in the Y node set. If edge I-> J exists, edge I-> J is introduced in the bipartite graph ', if the maximum matching value of a bipartite graph is m, the result is n-M.
Remember an important conclusion: the least path overwrite count of the DAC graph = number of nodes (N)-maximum match count

Code:

#include<cstdio>#include<cstring>#include<queue>#include<vector>#include<cmath>#include<iostream>#include<algorithm>using namespace std;vector<int>V[1000];int link[1000],use[1000];void init(int n){    int i;    for(i=0;i<=n;i++)      V[i].clear();}bool Dfs(int v){    int i,j,k;    for(i=0;i<V[v].size();i++)    {        k=V[v][i];        if(!use[k])        {            use[k]=1;            if(!link[k]||Dfs(link[k]))            {                link[k]=v;                return true;            }        }    }    return false;}struct hh{    int x;    int y;    int x1,x2,y1,y2;}map[1000];int MaxMatch(int n){    int i,j,ans=0;    memset(link,0,sizeof(link));    for(i=1;i<=n;i++)    {        memset(use,0,sizeof(use));        if(Dfs(i))            ans++;    }    return ans;}int Find(int i,int j,int x,int y){    return abs(i-j)+abs(x-y);}int main(){    int i,j,n,m,k,t;    scanf("%d",&t);    while(t--)    {        int x1,y1,x2,y2;        scanf("%d",&n);        init(n);        for(i=1;i<=n;i++)        {            scanf("%d:%d %d%d%d%d",&m,&k,&map[i].x1,&map[i].y1,&map[i].x2,&map[i].y2);            map[i].x=m*60+k;            map[i].y=map[i].x+Find(map[i].x1,map[i].x2,map[i].y1,map[i].y2);        }        for(i=1;i<n;i++)        {            for(j=i+1;j<=n;j++)              if(map[i].y+Find(map[i].x2,map[j].x1,map[i].y2,map[j].y1)<map[j].x)                 V[i].push_back(j);        }        int ans=MaxMatch(n);        printf("%d\n",n-ans);    }}