leetcode findNthDigit
z
 2019-04-09 10:36:27   
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public class NthDigit {
  public int findNthDigit(int n) {
    /**
     * Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...
     * Note:
     * n is positive and will fit within the range of a 32-bit signed integer (n < 231).
     * Example 1:
     * Input:
     * 3
     * Output:
     * 3
     * Example 2:
     *
     * Input:
     * 11
     *
     * Output:
     * 0
     *
     * Explanation:
     * The 11th digit of the sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ... is a 0, which is part of the number 10.
     *
     * 			width count
     * 		  1-9:  1     9
     * 	    10-99:  2    90
     *      100-999:  3   900
     *
     *      w, c = 1, 9 // width and count of numbers (of each level)
     *      while n > w*c:
     *         n -= w*c
     *         w += 1
     *         c *= 10
     *      num, d = (c/9) + (n-1)/w, (n-1)%w       // c/9 is equals to 10**w, means the base number
     *      return int(str(num)[d])
     */
    if (n < 10) {
      return n;
    } else if (n < 100) {
      if (n % 2 == 0) {
        return n;
      }
    }
    return n;
  }
}