codeforces 520B Two Buttons BFS

B. Two Buttons

time limit per test
2 seconds

memory limit per test
256 megabytes

input
standard input

output
standard output

Vasya has found a strange device. On the front panel of a device there are: a red button, a blue button and a display showing some positive integer. After clicking the red button, device multiplies the displayed number by two. After clicking the blue button,
device subtracts one from the number on the display. If at some point the number stops being positive, the device breaks down. The display can show arbitrarily large numbers. Initially, the display shows number
n.

Bob wants to get number m on the display. What minimum number of clicks he has to make in order to achieve this result?

Input
The first and the only line of the input contains two distinct integers
n and m (1 ≤ n, m ≤ 104), separated by a space .

Output
Print a single number — the minimum number of times one needs to push the button required to get the number
m out of number n.

Sample test(s)

Input

4 6

Output

2

Input

10 1

Output

9

Note
In the first example you need to push the blue button once, and then push the red button once.

In the second example, doubling the number is unnecessary, so we need to push the blue button nine times.

#include<vector>
#include<cstdio>
#include<iostream>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<stack>
#include<queue>
#include<set>
#define mem(a,x) memset(a,x,sizeof(a))
#define inf 0x3f3f3f3f
typedef long long ll;
using namespace std;

inline int in()
{
int res=0;char c;
while((c=getchar())<'0' || c>'9');
while(c>='0' && c<='9')res=res*10+c-'0',c=getchar();
return res;
}
int vis[10009];
void bfs(int n,int m)
{
queue<int> q;
q.push(n);
vis
=0;
while(!q.empty())
{
int now=q.front();
q.pop();
int tmp=now-1;
if(tmp>0 && vis[tmp]==inf)
{
vis[tmp]=vis[now]+1;
if(tmp==m)return;
q.push(tmp);

}
tmp=now*2;
if(tmp>0 && vis[tmp]==inf)
{
vis[tmp]=vis[now]+1;
if(tmp==m)return;
q.push(tmp);
}

}
}
int main()
{
int n=in(),m=in();
mem(vis,inf);
bfs(n,m);
cout<<vis[m];

return 0;
}