A - Til the Cows Come Home

A - Til the Cows Come Home
Time Limit:1000MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u
Submit Status Practice POJ 2387

Description
Bessie is out in the field and wants to get back to the barn to get as much sleep as possible before Farmer
 John wakes her for the morning milking. Bessie needs her beauty sleep, so she wants to get back as quickly
  as possible.

Farmer John's field has N (2 <= N <= 1000) landmarks in it, uniquely numbered 1..N.
Landmark 1 is the barn; the apple tree grove in which Bessie stands all day is landmark N.
 Cows travel in the field using T (1 <= T <= 2000) bidirectional cow-trails of various lengths between
  the landmarks. Bessie is not confident of her navigation ability, so she always stays on a trail
  from its start to its end once she starts it.

Given the trails between the landmarks, determine the minimum distance Bessie must walk to get
back to the barn. It is guaranteed that some such route exists.

Input
* Line 1: Two integers: T and N

* Lines 2..T+1: Each line describes a trail as three space-separated integers.
The first two integers are the landmarks between which the trail travels.
The third integer is the length of the trail, range 1..100.

Output
* Line 1: A single integer, the minimum distance that Bessie must travel to get from landmark
N to landmark 1.

Sample Input

5 5
1 2 20
2 3 30
3 4 20
4 5 20
1 5 100

Sample Output

90

#include <stdio.h>
#include <string.h>
#define inf 0x3f3f3f3f
#define Max 1005
int dist[Max];
int g[Max][Max];
int used[Max];
int n,m,i;
void add_edge(int a,int b,int c)
{
	if(g[a][b]>c)
	{
		g[a][b] = g[b][a] = c;
	}
}
void init()
{
	memset(used,0,sizeof(used));
	memset(dist,inf,sizeof(dist));
}
void Dijkstra(int begin)
{
	init();
	dist[begin] = 0;
	while(1)
	{
		int min = inf,u=-1,v;
		for(i=1;i<=n;i++)
		{
			if(min>dist[i] && !used[i])
			{
				min = dist[i];
				u = i;
			}
		}
		used[u] = 1;
		if(u==-1)
		{
			break;
		}
		for(v=1;v<=n;v++)
		{
			if(!used[v] && dist[v]>dist[u]+g[u][v])
			{
				dist[v] = dist[u] + g[u][v];
			}
		}
		
	}
}
int main()
{
	while(scanf("%d%d",&m,&n)!=EOF)
	{
		int a, b, c;
		memset(g,inf,sizeof(g));
		for(i=1;i<=m;i++)
		{
			scanf("%d%d%d",&a,&b,&c);
			add_edge(a,b,c);
		}
		Dijkstra(1);
		printf("%d\n",dist[n]);
	}
	return 0;
}