题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=2717
题解：一维简单BFS，详细看代码，0ms。
1 #include<cstdio> 2 #include<queue> 3 using namespace std; 4 const int maxn=100002; 5 bool v[maxn]; 6 int n,k; 7 struct nd{ 8 int x,step; 9 }; 10 bool check(int x){ 11 if(x<0||x>100000||v[x])return false; 12 else return true; 13 } 14 int bfs(int s){ 15 for(int i=0;i<=100000;i++)v[i]=false;//初始化标记 16 queue<nd>Q; 17 nd S; 18 S.x=s,S.step=0; 19 v[s]=1; 20 Q.push(S); 21 while(!Q.empty()){ 22 nd now=Q.front();Q.pop(); 23 if(now.x==k)return now.step; 24 if(check(now.x+1)){ 25 nd tmp;tmp.x=now.x+1,tmp.step=now.step+1; 26 v[tmp.x]=1; 27 Q.push(tmp); 28 } 29 if(check(now.x-1)){ 30 nd tmp;tmp.x=now.x-1,tmp.step=now.step+1; 31 v[tmp.x]=1; 32 Q.push(tmp); 33 } 34 if(check(now.x*2)){ 35 nd tmp;tmp.x=now.x*2,tmp.step=now.step+1; 36 v[tmp.x]=1; 37 Q.push(tmp); 38 } 39 } 40 return -1; 41 } 42 int main(){ 43 while(~scanf("%d%d",&n,&k)){ 44 if(n>=k){printf("%d ",n-k);continue;}//剪枝 45 int ans=bfs(n); 46 printf("%d ",ans); 47 } 48 return 0; 49 }