acer 生涯的第一道Bfs,终于ac了。刚开始与深搜弄混了，自己也晕了一上午。（）
还有就是queue中几个函数的用法；
pop()//删除队首元素
front()获得队首元素
push()//
back(),empty()//
1 #include <iostream>
2 #include <queue>//注意与<queue.h>的区别
3 using namespace std;
4 const int Max=100001;
5 queue <int>q;
6 int used[Max];
7 int step[Max];
8 int totle;
9 void Bfs(int k,int s,int e)
10 {
11
12
13 while(!q.empty())
14 {
15 int n;
16 int head;
17 head=q.front();
18 //cout<<"head:"<<head<<endl;
19 q.pop();
20 if(head==k)
21 break;
22 n=head;
23 //used[n]=1;
24 if(n-1>=0&&!used[n-1])
25 {
26 q.push(n-1);
27 used[n-1]=1;
28 step[n-1]=step[n]+1;
29 }
30 if(n+1<=e&&!used[n+1])
31 {
32 q.push(n+1),used[n+1]=1;
33 step[n+1]=step[n]+1;
34 }
35 if(n*2<=e&&!used[n*2])
36 {
37 q.push(n*2),used[n*2]=1;
38 step[n*2]=step[n]+1;
39 }
40
41 }
42
43 }
44 int main()
45 {
46 int k,n;
47 while(cin>>n>>k)
48 {
49 if(n>=k)
50 cout<<n-k<<endl;
51 else
52 {
53 while(!q.empty())
54 q.pop();
55
56 memset(step,0,sizeof(step));
57 memset(used,0,sizeof(used));
58 used[n]=1;
59 step[n]=0;
60 totle=n+(k-n)*2;
61 if(totle>100000)
62 totle=100000;
63 /*if(n-1>=0&&!used[n-1])
64 {q.push(n-1);used[n-1]=1;step[n-1]=step[n]+1;}
65 if(n+1<=totle&&!used[n+1])
66 {q.push(n+1);used[n+1]=1;step[n+1]=step[n]+1;}
67 if(n*2<=totle&&!used[n*2])
68 {q.push(n*2),used[n*2]=1;step[n*2]=step[n]+1;}
69 int head=q.front();
70 q.pop();
71 */
72 q.push(n);
73 Bfs(k,0,totle);
74 cout<<step[k]<<endl;
75 //head=q.front();
76 //cout<<head<<endl;
77
78 }
79 }
80 return 0;
81
82 }