Codeforces Beta Round #9 (Div. 2 Only) C. Hexadecimal's Numbers dfs

2024-04-17 06:19:01

C. Hexadecimal's Numbers

题目连接：

http://www.codeforces.com/contest/9/problem/C

Description

One beautiful July morning a terrible thing happened in Mainframe: a mean virus Megabyte somehow got access to the memory of his not less mean sister Hexadecimal. He loaded there a huge amount of n different natural numbers from 1 to n to obtain total control over her energy.

But his plan failed. The reason for this was very simple: Hexadecimal didn't perceive any information, apart from numbers written in binary format. This means that if a number in a decimal representation contained characters apart from 0 and 1, it was not stored in the memory. Now Megabyte wants to know, how many numbers were loaded successfully.

Input

Input data contains the only number n (1 ≤ n ≤ 109).

Output

Output the only number — answer to the problem.

Sample Input

10

Sample Output

2

Hint

题意

问你小于等于n的数里面，有多少个只由0和1组成的

题解：

感觉上没多少个数嘛，那就直接dfs就好了啦

代码

#include<bits/stdc++.h>
using namespace std;
long long n;
map<int,int> vis;
long long ans = 0;
void dfs(long long x)
{if(x>n)return;if(vis[x])return;vis[x]=1;ans++;dfs(x*10);dfs(x*10+1);
}
int main()
{cin>>n;dfs(1);cout<<ans<<endl;
}

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