leetcode 357 Count Numbers with Unique Digits
z
 2019-04-09 10:36:27  

Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.

Example:

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Input: 2
Output: 91 
Explanation: The answer should be the total numbers in the range of 0 ≤ x < 100, 
             excluding 11,22,33,44,55,66,77,88,99
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public class CountNumberswithUniqueDigits {
  /*
      Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10^n.
      Example:

      Input: 2
      Output: 91
      Explanation: The answer should be the total numbers in the range of 0 ≤ x < 100, excluding 11,22,33,44,55,66,77,88,99
   */
  public int countNumbersWithUniqueDigits(int n) {
    if (n<1){
      return 1;
    }
    else if (n==1){
      return 10;
    }
    else if (n>10){
      n = 10;
    }
    return countNumbersWithUniqueDigits(n-1) + (countNumbersWithUniqueDigits(n-1) - countNumbersWithUniqueDigits(n-2)) * (10-(n-1));
  }
}```