图练习-BFS-从起点到目标点的最短步数

http://acm.sdut.edu.cn/sdutoj/problem.php?action=showproblem&problemid=2830

简单bfs

 #include <stdio.h>
 #include <string.h>
 #include <algorithm>
 #include <queue>
 using namespace std;
 const int N=;
 int head[N],vis[N];
 int cnt = ;
 struct Edge
 {
     int u,v;
     int next;
 } edge[*N];
 struct node
 {
     int x,step;
     node(int x,int step):x(x),step(step) {}
 };
 void add(int u,int v)
 {
     edge[cnt].u = u;
     edge[cnt].v = v;
     edge[cnt].next = head[u];
     head[u] = cnt++;
 }
 int bfs(int n)
 {
     memset(vis,,sizeof(vis));
     queue<node>q;
     node s(n,);
     q.push(s);
     vis[n] = ;
     while(!q.empty())
     {
         node u = q.front();
         q.pop();
         if (u.x==)
             return u.step;
         for (int j = head[u.x]; j!=-; j=edge[j].next)
         {
             int v = edge[j].v;
             if (!vis[v])
             {
                 q.push(node(v,u.step+));
                 vis[v] = ;
             }
         }
     }
     return -;
 }
 int main()
 {
     int n,m;
     int u,v;
     while(~scanf("%d%d",&n,&m))
     {
         cnt = ;
         memset(vis,,sizeof(vis));
         memset(head,-,sizeof(head));
         for (int i = ; i < m; i++)
         {
             scanf("%d%d",&u,&v);
             add(u,v);
             add(v,u);
         }
         int ans = bfs(n);
         if (ans==-)
             puts("NO");
         else
             printf("%d\n",ans);
     }
     return ;
 }