题目链接：点击打开链接
#include<stdio.h>
#include<iostream>
#include<string.h>
#include<set>
#include<vector>
#include<map>
#include<math.h>
#include<string>
#include<stdlib.h>
#include<algorithm>
using namespace std;
#define N 1000005
#define ll __int64
ll num[10],n;
ll go(ll x){
ll ans = x;
while(ans>=10){
ans = 0;
while(x) {
ans += x%10;
x /= 10;
}
x = ans;
}
return ans;
}
int main(){
ll i,j,k;
while(~scanf("%I64d",&n))
{
memset(num, 0, sizeof num);
ll ans = 0;
for(i=1;i<=n;i++) num[go(i)]++, ans -= n/i;
for(j=0;j<10;j++)
for(k=0;k<10;k++)
ans+=num[k]*num[j]*num[go(k*j)];
printf("%I64d\n",ans);
}
return 0;
}
/*
2
1 2
3
1 2 3
*/Codeforces 10C Digital Root 规律题,布布扣,bubuko.com
Codeforces 10C Digital Root 规律题
原文：http://blog.csdn.net/qq574857122/article/details/34469589