POJ 1797 Heavy Transportation【并查集+贪心】

Heavy Transportation
Time Limit: 3000MS
 
Memory Limit: 30000K
Total Submissions: 50413
 
Accepted: 13007
Description
Background  Hugo Heavy is happy. After the breakdown of the Cargolifter project he can now expand business. But he needs a clever man who tells him whether there really is a way from the place his customer has build his giant steel crane to the place where it is needed on which all streets can carry the weight.  Fortunately he already has a plan of the city with all streets and bridges and all the allowed weights.Unfortunately he has no idea how to find the the maximum weight capacity in order to tell his customer how heavy the crane may become. But you surely know.  Problem  You are given the plan of the city, described by the streets (with weight limits) between the crossings, which are numbered from 1 to n. Your task is to find the maximum weight that can be transported from crossing 1 (Hugo's place) to crossing n (the customer's place). You may assume that there is at least one path. All streets can be travelled in both directions.
Input
The first line contains the number of scenarios (city plans). For each city the number n of street crossings (1 <= n <= 1000) and number m of streets are given on the first line. The following m lines contain triples of integers specifying start and end crossing of the street and the maximum allowed weight, which is positive and not larger than 1000000. There will be at most one street between each pair of crossings.
Output
The output for every scenario begins with a line containing "Scenario #i:", where i is the number of the scenario starting at 1. Then print a single line containing the maximum allowed weight that Hugo can transport to the customer. Terminate the output for the scenario with a blank line.
Sample Input

1
3 3
1 2 3
1 3 4
2 3 5

Sample Output

Scenario #1:
4

Source
TUD Programming Contest 2004, Darmstadt, Germany
質問リンク:POJ 1797 Heavy Transportation
質問説明:指定されたn個の交差点(1から番号付け)にはm個の双方向の街リンクがあり、各街には最大荷重があり、1番のノードからn番のノードまでの路線案の中で、最小荷重の街の最大値はいくらですか.
解題の構想:そして集+貪欲を調べて、辺の最大の荷重によって大きいから小さいまで辺をプラスして、1番の結点とn番の結点を連通させるまで
ACのC++プログラム:

#include
#include
#include

using namespace std;

const int N=1005;

int pre[N];

//      ：             
void init(int n)
{
	for(int i=1;i<=n;i++)
	  pre[i]=i;
} 

int find(int x)
{
	int r=x;
	while(r!=pre[r])
	  r=pre[r];
	//    
	while(x!=r){
		int i=pre[x];
		pre[x]=r;
		x=i;
	}
	return r; 
}

struct Edge{
	int u,v,c;
	bool operatora.c;
	}
}e[N*N/2];

void join(int x,int y)
{
	int fx=find(x);
	int fy=find(y);
	if(fx!=fy)
	  pre[fx]=fy;
} 

int main()
{
	int T,n,m;
	scanf("%d",&T);
	for(int t=1;t<=T;t++){
		scanf("%d%d",&n,&m);
		for(int i=0;i