题解 |从1到n整数中1出现的次数#

class Solution {
public:
    int NumberOf1Between1AndN_Solution(int n) {
        long base=1;
        long res=0;
        while(base<=n){
            long cur=(n/base)%10;
            long low=n%base;
            long high=n/base/10;

            if (cur>1) {
                res+=(high+1)*base;
            }else if(cur==1){
                res+=(high*base)+(1+low);
            }else {
                res+=high*base;
            }
            base=base*10;
        }
        return (int)res;
    }
};