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    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.

    Example
    Input
    10
    Output
    2
    Note

    For n = 10 the answer includes numbers 1 and 10.

    题目分析 : 给你一个 n ,表示 1 - n 共 n 个数字,问有多少个数字中只含有 0 和 1

    思路分析 : 对于一个只含有 01 数字的十进制数字,他一定可以通过这样的变换得来, a*10 和 a*10+1 , 既然有这样的规律,那么写一个深搜就可以直接过了。

    代码示例 :

      

    int ans = 0;
    ll n;
    
    void dfs(ll x){
        if (x > n) return;
        ans++;
        dfs(x*10);
        dfs(x*10+1);
    }
    
    int main() {   
        cin >> n;
        dfs(1);
        printf("%d
    ", ans);
        
        return 0;
    }
    
    东北日出西边雨 道是无情却有情
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  • 原文地址:https://www.cnblogs.com/ccut-ry/p/8321306.html
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