Til the Cows Come Home

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mb612e31a113ff5 2022-06-05 00:41:20 ©著作权

文章标签 #include i++ 最短路径 文章分类 Java 后端开发

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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

Sample Output

Hint

INPUT DETAILS:

There are five landmarks.

OUTPUT DETAILS:

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

题解：此题为基本为版子题，是求N到1的最短路，解决思路为建个双向图，直接求以为N源点，到1的最短路径代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#define Inf 0x3f3f3f3f

using namespace std;

int map[1005][1005];

int vis[1005],dis[1005];
int n,m;

void Init ()
{
    memset(map,Inf,sizeof(map));
    for(int i=1;i<=n;i++)
    {
        map[i][i]=0;
    }
}

void Getmap()
{
    int u,v,w;
    for(int t=1;t<=m;t++)
    {
          scanf("%d%d%d",&u,&v,&w);
          if(map[u][v]>w)
          {
          map[u][v]=w;
          map[v][u]=w;
          }
    }    
    
}

void Dijkstra(int u)
{
    memset(vis,0,sizeof(vis));
    for(int t=1;t<=n;t++)
    {
        dis[t]=map[u][t];
    }
    vis[u]=1;
    for(int t=1;t<n;t++)
    {
        int minn=Inf,temp;
        for(int i=1;i<=n;i++)
        {
            if(!vis[i]&&dis[i]<minn)
            {
                minn=dis[i];
                temp=i;
            }
        }
        vis[temp]=1;
        for(int i=1;i<=n;i++)
        {
            if(map[temp][i]+dis[temp]<dis[i])
            {
                dis[i]=map[temp][i]+dis[temp];
            }
        }
    }
    
}

int main()
{
    
    scanf("%d%d",&m,&n);
    Init();
    Getmap();
    Dijkstra(n);
    printf("%d\n",dis[1]);
    
    
    return 0;
}