Array of Doubled Pairs — LeetCode 954 Python Solution

The problem

Given an integer array of even length arr, return true if it is possible to reorder arr such that arr[2 * i + 1] = 2 * arr[2 * i] for every 0 <= i < len(arr) / 2, or false otherwise.

Example

Input

arr = [3,1,3,6]

Output

false

Python solution

class Solution:
    def canReorderDoubled(self, arr: List[int]) -> bool:
        freq = Counter(arr)
        if freq[0] & 1:
            return False
        for x in sorted(freq, key=abs):
            if freq[x << 1] < freq[x]:
                return False
            freq[x << 1] -= freq[x]
        return True

Complexity

Pattern: Greedy

Take the locally best option every time — when you can prove that never costs you later. LeetCode 954. Array of Doubled Pairs is filed here because LeetCode tags it Greedy, which is the vocabulary this hub collects.

The greedy guide has the Python template for the pattern and the 346 LeetCode problems that use it.

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