# POJ 2387 Til the Cows Come Home（Dijkstra判重边）

2015年2月24日 10点热度 0条评论 来源: wikioi_bai

Til the Cows Come Home

 Time Limit: 1000MS Memory Limit: 65536K Total Submissions: 31748 Accepted: 10757

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`

Hint

INPUT DETAILS:

There are five landmarks.

OUTPUT DETAILS:

Bessie can get home by following trails 4, 3, 2, and 1.

Source

``````# include<cstdio>
# include<iostream>

using namespace std;

# define MAX 1000+4
# define inf 99999999

int n,t;
int edge[MAX][MAX];
int dis[MAX];
int book[MAX];
int u,v;

void init()
{
for ( int i = 1;i <= n;i++ )
{
for ( int j = 1;j <= n;j++ )
{
if ( i==j )
{
edge[i][j] = 0;
}
else
{
edge[i][j] = inf;
}
}
}
}

void input()
{
for ( int i = 0;i < t;i++ )
{
int t1,t2,t3;
cin>>t1>>t2>>t3;
if ( t3 < edge[t1][t2] )
{
edge[t1][t2] = t3;
edge[t2][t1] = t3;
}
}

}

void Dijkstra()
{
for ( int i = 1;i <= n;i++ )
{
book[i] = 0;
dis[i] = edge[n][i];
}

int _min;
for ( int i = 1;i <= n-1;i++ )
{
_min = inf;
for ( int j = 1;j <= n;j++ )
{
if ( book[j]==0&&dis[j] < _min )
{
_min = dis[j];
u = j;
}
}

book[u] = 1;
for ( v = 1;v <= n;v++ )
{
if ( book[v]==0&&dis[v] > dis[u]+edge[u][v] )
{
dis[v] = dis[u]+edge[u][v];
}
}

}
}

int main(void)
{
while ( cin>>t>>n )
{
init();
input();
Dijkstra();
cout<<dis<<endl;

}

return 0;
}
``````

原文作者：wikioi_bai
原文地址: https://blog.csdn.net/wikioi_bai/article/details/43924799
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