面试题43. 1～n 整数中 1 出现的次数

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; 
    }
}