题目
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.
解题思路
贪心，使用计数器求出每个数出现的次数，然后按绝对值从小到大，如果当前数为n，查看2n出现的次数是否大于等于n
代码
class Solution:
def canReorderDoubled(self, arr: List[int]) -> bool:
ct = collections.Counter(arr)
for n in sorted(ct, key=abs):
if ct[n] > ct[2 * n]:
return False
ct[2 * n] -= ct[n]
return True
