hdu 1102 Constructing Roads（Kruskal算法）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1102

Constructing Roads

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 17132    Accepted Submission(s): 6500

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

注意并查集的初始化 MakeSet， 注意Kruskal 算法与边有关，储存边的数组要开到 N^2;

【代码】

#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 110;
const int maxe =10010;
struct node{
	int V1,V2, len ;
}edge[maxe];
int father[maxn];
bool cmp(const node &a, const node& b){
	return a.len<b.len;
}
void MakeSet(){
	for(int i=0;i<maxn;i++)
		father[i]=i;
}
int Find(int x){
	
	int root = x;
	while(root!=father[root])
		root = father[root];
	while(x!=root){
		int tmp = father[x];
		father[x] = root;
		x = tmp;
	}
	return root;
}
void Union(int x,int y){
	int xr = Find(x);
	int yr = Find(y);
	if(xr==yr) return ;
	father[xr]=yr;
}
int cnt;	int n;
void Kruskal(){
	int edgenum=0;
	int ans=0;
	for(int i=0;i<cnt &&edgenum!=n-1;i++){
		if(Find(edge[i].V1)!=Find(edge[i].V2)){
			ans+=edge[i].len;
			Union(edge[i].V1,edge[i].V2);
		}
	}
	cout<<ans<<endl;
}
int main(){

	while(cin>>n){
		int dis;
		cnt=0;
		MakeSet();
		for(int i=0;i<n;i++){
			for(int j=0;j<n;j++){
				cin>>dis;
				if(j==i) continue;
				edge[cnt].V1 = i;
				edge[cnt].V2 = j;
				edge[cnt].len = dis;
				cnt++;
			}
		}
		sort(edge,edge+cnt,cmp);
		int t,v1,v2;
		cin>>t; 
		for(int i=0;i<t;i++){
			cin>>v1>>v2;
			Union(v1-1,v2-1);
		}
		Kruskal();
	}
	return 0;
}