POJ 2387 Til the Cows Come Home

Posted 2020-09-28

题目描述

给定的n个点中有m条边，求从1到n之间的最短距离。

 

题解

裸的，bellman-Ford 或者spfa就好了。好久没打最短路了随手打了一下。

 

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cmath>
 6 #include<queue>
 7 using namespace std;
 8 const int INF = 1e9;
 9 const int M = 1000 + 10;
10 int to[M * 2], nxt[M * 2], w[M * 2];
11 int head[M * 2], tot;
12 int dis[M * 2];
13 int m, n; 
14 void add(int u,int v,int c)
15 {
16     w[tot] = c;
17     to[tot] = v;
18     nxt[tot] = head[u];
19     head[u] = tot++;
20 }
21 void spfa(int s)
22 {
23     bool vis[M];
24     memset(vis, false, sizeof(vis));
25     queue<int> q;
26     for(int i=0; i<=n; i++)
27         dis[i]=INF;
28     q.push(s);
29     dis[s] = 0;
30     vis[s] = true;
31     while(!q.empty())
32     {
33         int u = q.front();
34         q.pop();
35         for(int i = head[u]; i != -1; i = nxt[i])
36         {
37             int v = to[i];
38             if(dis[v] > dis[u] + w[i])
39             {
40                 dis[v] = dis[u] + w[i];
41                 if(!vis[v])
42                 {
43                     vis[s] = true;
44                     q.push(v);
45                 }
46             }
47         }
48     }
49 }
50 int main()
51 {
52     scanf("%d%d", &m, &n);
53     memset(head,-1,sizeof(head));
54     while(m--)
55     {
56         int u,v,c;
57         scanf("%d%d%d",&u,&v,&c);
58         add(u,v,c);
59         add(v,u,c);
60     }
61     spfa(1); 
62     printf("%d\n",dis[n]);
63     return 0;
64 }