leetcode随机刷题记录 面试题17.06.2出现的次数

思路，每次只计算到了当前位的时候，当前位为2的时候有多少可能的数

class Solution {
public:
    int numberOf2sInRange(int n) {
        if(n < 2){
            return 0;
        }else if(n <= 10){
            return 1;
        }
        long long xl;
        long long xr;
        long long xm;
        int an = 0;
        for(long long i = 1; ; i *= 10){
            xl = n / i;
            if(xl == 0){
                break;
            }
            xm = xl % 10;
            xl /= 10;
            xr = n % i;
            if(xl == 0){
                if(xm > 2){
                    xr = i;
                    an += xr;
                }else if(xm == 2){
                    an += xr + 1;
                }
            }else{
                if(xm > 2){
                    xr = i;
                    an += xr;
                }else if(xm == 2){
                    an += xr + 1;
                }
                xr = i;
                an += xl * xr;
            }
       //     cout << xl << " " << xr << " " << an << endl;
        }
            
        return an;
    }
};