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529. Duplicate even elements in an array

Given an array of numbers, write a program to duplicate the even numbers and return the new array.

Example:

Input: [2, 4, 1, 5, 2, 3, 8, 9, 10, 4]
Output: [2, 2, 4, 4, 1, 5, 2, 2, 3, 8, 8, 9, 10, 10, 4, 4]

Input: [2, 4, 6, 8]
Output: [2, 2, 4, 4, 6, 6, 8, 8]

Input: [1, 3, 5, 6]
Output: [1, 3, 5, 6, 6]

Approach:

  1. Iterate the input array and count the number of even numbers.
  2. Initialize result of array of size newLength-1 = input array + evenCount (for even number).
  3. Initialize index = newLength-1.
  4. Now iterate the array from right to left and for the current element
    1. If the current element is odd then copy the current element to the result[index].
    2. If the current element is even then copy the current element to the result[index] and result[--index]. 
    3. Do index = index - 1.
  5. Return the result array.

Time Complexity: O(N)

Output:

Input: [2, 4, 1, 5, 2, 3, 8, 9, 10, 4]
Output: [2, 2, 4, 4, 1, 5, 2, 2, 3, 8, 8, 9, 10, 10, 4, 4]
------------------------
Input: [2, 4, 6, 8]
Output: [2, 2, 4, 4, 6, 6, 8, 8]
------------------------
Input: [1, 3, 5, 6]
Output: [1, 3, 5, 6, 6]

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