Problem Statement
You are given an integer N. Among the integers between 1 and N (inclusive), how many Shichi-Go-San numbers (literally "Seven-Five-Three numbers") are there?
Here, a Shichi-Go-San number is a positive integer that satisfies the following condition:
- When the number is written in base ten, each of the digits
7
,5
and3
appears at least once, and the other digits never appear.
Constraints
- 1≤N<109
N is an integer.
Input
Input is given from Standard Input in the following format:
N
Output
Print the number of the Shichi-Go-San numbers between 1 and N (inclusive).
Sample Input 1
575
Sample Output 1
4
There are four Shichi-Go-San numbers not greater than 575: 357,375,537 and 573.
Sample Input 2
3600
Sample Output 2
13
There are 13 Shichi-Go-San numbers not greater than 3600: the above four numbers, 735,753,3357,3375,3537,3557,3573,3575 and 3577.
Sample Input 3
999999999
Sample Output 3
26484
题目大意:
给您一个整数N。在1到N(含)之间的整数中,有多少个只包含 数字3,5,7且都至少出现一次
题解:
从零开始,等于每次加在尾数加三或者五,七之和(用三个bool类型表示3,5,7是否存在)
#include<iostream>
using namespace std;
long long n;
int dfs(long long x,bool A,bool B,bool C){
if(x>n) return 0;
long long ret=0;
if(A&&B&&C) ret++;
ret+=dfs(x*10+7,true,B,C);
ret+=dfs(x*10+5,A,true,C);
ret+=dfs(x*10+3,A,B,true) ;
return ret;
}
int main()
{
cin >> n;
cout << dfs(0,false,false,false)<<endl ;
return 0;
}