2007. Find Original Array From Doubled Array

Medium

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An integer array original is transformed into a doubled array changed by appending twice the value of every element in original, and then randomly shuffling the resulting array.

Given an array changed, return original if changed is a doubled array. If changed is not a doubled array, return an empty array. The elements in original may be returned in any order.

Example 1:

Input: changed = [1,3,4,2,6,8]
Output:
 [1,3,4]
Explanation:
 One possible original array could be [1,3,4]:
- Twice the value of 1 is 1 * 2 = 2.
- Twice the value of 3 is 3 * 2 = 6.
- Twice the value of 4 is 4 * 2 = 8.
Other original arrays could be [4,3,1] or [3,1,4].

Example 2:

Input: changed = [6,3,0,1]
Output:
 []
Explanation:
 changed is not a doubled array.

Example 3:

Input: changed = [1]
Output:
 []
Explanation:
 changed is not a doubled array.

Constraints:

• 1 <= changed.length <= 105

• 0 <= changed[i] <= 105

class Solution:
    def findOriginalArray(self, changed: List[int]) -> List[int]:
        counter = collections.Counter(changed)
        # Odd Zeroes
        if counter[0] % 2:
            return []
        for ele in sorted(counter):
            if counter[ele] > counter[ele*2]:
                return []
            counter[ele*2] -= counter[ele] if ele else counter[ele]//2
        return list(counter.elements())