233. 数字 1 的个数 2021-08-13

class Solution {
public:
    int countDigitOne(int n) {
        int count = 0;
        int high, low;
        long long digit;
        high = n;
        low = 0;
        digit = 1;
        while (high > 0) {
            int i = high % 10;
            high /= 10;
            count += (high * digit);
            if (i > 1)
                count += digit;
            else if (i == 1)
                count += (low + 1);
            digit *= 10;
            low = n % digit;
        }
        return count;
    }
};