题解 | 2的个数

class Count2 {
  public:
    int countNumberOf2s(int n) {
        // write code here
        int low = 0;
        int high = n / 10;
        int cur = n % 10;
        int digit = 1;
        int count = 0;
        while (high || cur) {
            if (cur < 2) {
                count += high * digit;
            } else if (cur == 2) {
                count += high * digit + 1 + low;
            } else {
                count += (high + 1) * digit;
            }
            low +=cur*digit;
            cur = high%10;
            high /=10;
            digit *=10;
           

        }
        return count;

    }
};