Til the Cows home (P2387)

这个题就是简单的最短路问题，找到从点1到点N之间的最短距离。

由于好久没有做，一开始就以我自己的想法写，发现各种WRONG，

后来才发现自己的一些逻辑错误，

解题大意：点1到点1的距离为1，然后用DIJ方法做，每一次末尾更新的

                时候就是更新的是每一个点到点1之间的最短距离，如果有

               多种结果，会选 最小的即可。

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<map>using namespace std;#define N 1001#define inf 1e9int way[N][N];int    t;int  n;int main(){int  i,j,k;cin>>t>>n;for (i=1;i<=n;i++)for (j=1;j<=n;j++)way[i][j]=inf;int  hi[N];while (t--){cin>>i>>j>>k;if (k<way[i][j]){way[i][j]=way[j][i]=k;}}bool vist[N];memset(vist,false,sizeof(vist));vist[1]=true;j=1;for (i=1;i<=n;i++)hi[i]=way[i][1];t=n-1;int   ans[N];for (i=1;i<=n;i++)ans[i]=inf;ans[1]=0;while (t--){int big=inf;for (i=1;i<=n;i++) if (!vist[i]&&big>hi[i]){big=hi[i];j=i;}vist[j]=true;//cout<<j<<endl;for (i=1;i<=n;i++) if (!vist[i]){hi[i]=min(hi[i],way[j][i]+hi[j]);}}cout<<hi[n]<<endl;}

Til the Cows Come Home

Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 21874 Accepted: 7300

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 51 2 202 3 303 4 204 5 201 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

USACO 2004 November