poj 3159 差分约束+spfa

差分约束第一题，想明白以后就可以建图了。由于此题数据特殊，队列优化的spfa会超时，可以改成用栈来优化。
 1 #include <algorithm>
 2 #include <iostream>
 3 #include <cstring>
 4 #include <cstdio>
 5 using namespace std;
 6 
 7 const int INF = 9999999;
 8 const int N = 30001;
 9 const int M = 150000;
10 int head[N];
11 int dist[N];
12 bool visit[N];
13 int n, m, e;
14 
15 struct Edge
16 {
17     int v, next, w;
18 } edge[M];
19 
20 void addEdge( int u, int v, int w )
21 {
22     edge[e].v = v;
23     edge[e].w = w;
24     edge[e].next = head[u];
25     head[u] = e++;
26 }
27 
28 void spfa( int s )
29 {
30     for ( int i = 1; i <= n; i++ )
31     {
32         dist[i] = INF;
33         visit[i] = false;
34     }
35     dist[s] = 0;
36     visit[s] = true;
37     int q[N], top = 0;
38     q[top++] = s;
39     while ( top )
40     {
41         int u = q[--top];
42         visit[u] = false;
43         for ( int j = head[u]; j != -1; j = edge[j].next )
44         {
45             int v = edge[j].v, w = edge[j].w;
46             if ( dist[v] > dist[u] + w )
47             {
48                 dist[v] = dist[u] + w;
49                 if ( !visit[v] )
50                 {
51                     q[top++] = v;
52                     visit[v] = true;
53                 }
54             }
55         }
56     }
57 }
58 
59 int main ()
60 {
61     while ( scanf("%d%d", &n, &m) != EOF )
62     {
63         e = 0;
64         memset( head, -1, sizeof(head) );
65         while ( m-- )
66         {
67             int u, v, w;
68             scanf("%d%d%d", &u, &v, &w);
69             addEdge( u, v, w );
70         }
71         spfa(1);
72         printf("%d
", dist[n]);
73     }
74     return 0;
75 }