poj 3278 bfs

#include <iostream>

using namespace std;

int N,K;
int vis[200005] = {0};
int q[200005];

void bfs()
{
    int front,rear;
    front = rear = 0;
    q[rear++] = N;
    vis[N] = 0;
    if( N == K) return;
    while(front <= rear)
    {
        int x = q[front++];
        if(x == K)
         return;
        if(x >= 1 && !vis[x-1]){
            q[rear++] = x - 1;
            vis[x-1] = vis[x] + 1;
        }
        if(x+1 <= K && !vis[x+1]){
            q[rear++] = x + 1;
            vis[x+1] = vis[x] + 1;
        }
        if(x <= K && !vis[2*x]){
            q[rear++] = 2*x;
            vis[2*x] = vis[x] + 1;
        }
    }
}

int main()
{
//    freopen("in.in","r",stdin);

    cin>>N>>K;
    bfs();
    cout<<vis[K]<<endl;
}