233. Number of Digit One

Posted 2020-07-25 我的名字叫周周

    /*
     * 233. Number of Digit One 
     * 12.12 by Mingyang 
     *找规律题，不看也罢
     */
    public int countDigitOne(int n) {
        int ones = 0;
        for (long m = 1; m <= n; m *= 10) {
            long a = n / m, b = n % m;
            ones += (a + 8) / 10 * m;
            if (a % 10 == 1)
                ones += b + 1;
        }
        return ones;
    }