题解 | #挑7#

双端开始走 速度快一点比起一般

#include<bits/stdc++.h>
using namespace std;
int main(void)
{
    int n,m;
    int count=0;
    cin>>n;
    if(n<7)
    {
        cout<<'0'<<endl;
        return 0;
    }
    m = n/2;
    for(int i=0;i<=m;i++)
    {
        if((n-i)!=i)
        if((n-i)%10 == 7 || (n-i)/10%10 ==7||(n-i)/100%10 ==7||(n-i)/1000%10 ==7||(n-i)/10000%10 ==7||(n-i)%7==0)
            count++;
        if(i>=7)
         if(i%10 == 7 || i/10%10 ==7||i/100%10 ==7||i/1000%10 ==7||i/10000%10 ==7||i%7==0)
            count++;
    }
    cout<<count;
}