题目：
Til the Cows Come Home
| Time Limit: 1000MS | Memory Limit: 65536K | |
| Total Submissions: 61857 | Accepted: 20985 |
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.
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.
* 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
题意：一个无向带权图有n个顶点，T条边。顶点序号从1到n。求序号为1的点到序号为n的顶点的最短路。
思路：单源最短路径。迪杰斯特拉算法模板。链式前向星存图。
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<queue>
#include<map>
#include<stack>typedef long long ll;using namespace std;int head[10010];
struct{int to;int w;int next;
}mapp[10010];int minlen[10010];
bool vis[10010];struct node{int n;int len;node(const int nn,const int lenn){n = nn;len = lenn;}friend bool operator< (node f1, node f2){if(f1.len != f2.len)return f1.len > f2.len;return f1.n > f2.n; }
};int main(){ios::sync_with_stdio(false);memset(head,0,sizeof(head));memset(mapp,0,sizeof(mapp));memset(vis,0,sizeof(vis));int t,n;cin>>t>>n;for(int i = 1 ; i<=2*t ; i++){int a,b,len;cin>>a>>b>>len;mapp[i].to = b;mapp[i].w = len;mapp[i].next = head[a];head[a] = i;i++;mapp[i].to = a;mapp[i].w = len;mapp[i].next = head[b];head[b] = i;} priority_queue<node> q;memset(minlen,-1,sizeof(minlen));minlen[1] = 0;q.push(node(1,0));while (!q.empty()){node temp = q.top() ; q.pop();vis[temp.n] = 1;if(minlen[temp.n]!=-1 && minlen[temp.n]<temp.len)continue;for(int i = head[temp.n] ; i!=0 ; i = mapp[i].next){int nxt = mapp[i].to;if(!vis[nxt]){if(minlen[nxt] == -1){minlen[nxt] = minlen[temp.n]+mapp[i].w;q.push(node(nxt,minlen[nxt]));}else if(minlen[nxt] > minlen[temp.n]+mapp[i].w){minlen[nxt] = minlen[temp.n]+mapp[i].w;q.push(node(nxt,minlen[nxt]));}}}}cout<<minlen[n]<<endl;return 0;
}