SPFA板子（前向星）

 1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 const int INF = 0x3f3f3f3f;
 5 
 6 struct node
 7 {
 8     int v, w, next;
 9 }edge[5000005];
10 int n, tot;
11 int head[1000005], dis[1000005];
12 bool vis[1000005];
13 
14 void add_edge(int u,int v,int w)
15 {
16     tot++;
17     edge[tot].v = v;
18     edge[tot].w = w;
19     edge[tot].next = head[u];
20     head[u]=tot;
21 }
22 
23 void spfa(int x)
24 {
25     queue <int> q;
26     for(int i=1;i<=n;i++)
27     {
28         dis[i] = INF;
29         vis[i] = 0;
30     }
31     dis[x] = 0;
32     vis[x] = 1;
33     q.push(x);
34     while(!q.empty())
35     {
36         int u = q.front();
37         q.pop();
38         vis[u] = 0;
39         for(int i=head[u]; i; i=edge[i].next)
40         {
41             int v = edge[i].v;
42             if(dis[v] > dis[u]+edge[i].w)
43             {
44                 dis[v] = dis[u]+edge[i].w;
45                 if(!vis[v])
46                 {
47                     vis[v] = 1;
48                     q.push(v);
49                 }
50             }
51         }
52     }
53 }
54 
55 int main()
56 {
57     int m;
58     ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
59     cin >> n >> m;
60     tot = 0;
61     while(m--)
62     {
63         int u, v;
64         cin >> u >> v;
65         add_edge(u, v, 1);
66         add_edge(v, u, 1);
67     }
68     spfa(1);
69     for(int i=1; i<=n; i++)
70     {
71         cout << i << " " << dis[i] << endl;
72     }
73     return 0;
74 }