POJ1797 Heavy Transportation

Heavy Transportation

Time Limit: 3000MS		Memory Limit: 30000K
Total Submissions: 27180		Accepted: 7275

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

这道题困了我两三天，不过也顺便将Dijkstra理解的透彻了一些，第一次错误，招了两个小时，最后是因为把全局变量在main函数里边又定义了一遍，=_=,,,,，第二次错误，就是自己的不细心了，

思路：还是裸的Dijkstra，只是把缩小变成了扩大，但是有的地方要处理好。

代码如下：

#include<iostream>
#include<cstdio>
#include<cstring>
#define MAXN 2005
using namespace std;

int n,m;
int dis[MAXN][MAXN];
int cost[MAXN];
bool vis[MAXN];

void Dijkstra(int start)
{
	memset(vis,0,sizeof(vis));
	for(int i=1;i<=n;i++)
        cost[i]=dis[start][i];
	cost[start]=0;vis[start]=1;
	for(int i=1;i<=n;i++)
	{
		int nm=-1,k;
		for(int j=1;j<=n;j++)
		{
			if(!vis[j] && cost[j]>nm)  //这里松弛，是进行找到最大的承重
			{
				nm=cost[j];
				k=j;
			}
		}
		vis[k]=true;
		for(int j=1;j<=n;j++)
		{
		    if(!vis[j] && cost[j]<min(dis[k][j],cost[k])) cost[j]=min(dis[k][j],cost[k]); //找到那个最大的
 		}
	}
}
int main()
{
	int t,ct=1;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d%d",&n,&m);
		memset(dis,-1,sizeof(dis));
		for(int i=1;i<=m;i++)
		{
			int x,y,cot;
			scanf("%d%d%d",&x,&y,&cot);
			dis[x][y]=dis[y][x]=cot;
		}
		Dijkstra(1);
		printf("Scenario #%d:\n",ct++);
		printf("%d\n\n",cost[n]);
	}
	return 0;
}