class Solution {
public int countDigitOne(int n) {
int ans = 0;
int digit = 1;
int high=n/10;
int low = 0;
int cur=n%10;
while(high!=0||cur!=0){
if(cur==0) ans+=digit*high;
else if(cur==1) ans+=high*digit+low+1;
else if(cur>1) ans+=(high+1)*digit;
low+=cur*digit;
digit*=10;
cur=high%10;
high/=10;
}
return ans;
}
}
