acm专题---最小生成树

kruscal(eloge):

题目来源：http://acm.hdu.edu.cn/showproblem.php?pid=1102

Problem Description

There are N villages, which are numbered from 1 to N, and you should build some roads such that every two villages can connect to each other. We say two village A and B are connected, if and only if there is a road between A and B, or there exists a village C such that there is a road between A and C, and C and B are connected.

We know that there are already some roads between some villages and your job is the build some roads such that all the villages are connect and the length of all the roads built is minimum.

 

Input

The first line is an integer N (3 <= N <= 100), which is the number of villages. Then come N lines, the i-th of which contains N integers, and the j-th of these N integers is the distance (the distance should be an integer within [1, 1000]) between village i and village j.

Then there is an integer Q (0 <= Q <= N * (N + 1) / 2). Then come Q lines, each line contains two integers a and b (1 <= a < b <= N), which means the road between village a and village b has been built.

 

Output

You should output a line contains an integer, which is the length of all the roads to be built such that all the villages are connected, and this value is minimum. 

 

Sample Input

3
0 990 692
990 0 179
692 179 0
1
1 2

 

Sample Output

179

#include <iostream>
using namespace std;
#include <vector>
#include<algorithm>
#include<queue>
#include<string>
#include<map>
#include<math.h>
#include<iomanip>
#include<stack>
#include<string.h>
 
const int maxnum=101;
int mymap[maxnum][maxnum];
int n;
int fa[maxnum];
struct edge{
    int point1;
    int point2;
    int weight;
    edge(int _point1,int _point2,int _weight)
    {
        point1=_point1;
        point2=_point2;
        weight=_weight;
    }
};
int cmp(edge a,edge b)
{
    return a.weight<b.weight;
}
int findfa(int x)
{
    return fa[x]==x?x:(fa[x]=findfa(fa[x]));
}
 
void mergefa(int x,int y)
{
    fa[findfa(x)]=findfa(fa[y]);
}
 
void kruscal()
{
    vector<edge> edges;
 
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<i;j++)
        {
            edges.push_back(edge(i,j,mymap[i][j]));
        }
    }
    sort(edges.begin(),edges.end(),cmp);
 
    int m=n*(n-1)/2;
    int cnt=0;
    int ans=0;
    for(int i=0;i<m;i++)
    {
        int x1=edges[i].point1;
        int x2=edges[i].point2;
        int fa1=findfa(x1);
        int fa2=findfa(x2);
 
        if(fa1!=fa2)
        {
            mergefa(x1,x2);
            cnt+=1;
            ans+=edges[i].weight;
            if(cnt>=n-1) break;
        }
    }
 
    cout<<ans<<endl;
 
}
int main()
{
 
    while(cin>>n)
    {
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<n;j++)
            {
                cin>>mymap[i][j];
            }
        }
        for(int i=0;i<=n;i++)
            fa[i]=i;
        int m;
        cin>>m;
        for(int i=0;i<m;i++)
        {
            int x,y;
            cin>>x>>y;
            mymap[x-1][y-1]=mymap[y-1][x-1]=0;
 
        }
        kruscal();
 
    }
    return 0;
}
 
/*
 
 Sample Input
 3
 0 990 692
 990 0 179
 692 179 0
 1
 1 2
 
 Sample Output
 179
 
 */