leetcode 954. Array of Doubled Pairs

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 1:

Input: arr = [3,1,3,6]Output: false

Example 2:

Input: arr = [2,1,2,6]Output: false

Example 3:

Input: arr = [4,-2,2,-4]Output: trueExplanation: We can take two groups, [-2,-4] and [2,4] to form [-2,-4,2,4] or [2,4,-2,-4].

Constraints:

• 2 <= arr.length <= 3 * 104

• arr.length is even.

• -105 <= arr[i] <= 105

第一次用treemap.

treemap实现了sort的接口，所以可以直接排序完成，对于小的数（>0），去判断他的2倍数是否也在map中，而且小的数的value值应该要小于等于2倍数的value值，依次loop即可；

对于负数（<0）则判断它一半大小的值是否在map中，同时value值小于等于一半大小的value值。loop 结果；

Runtime: 42 ms, faster than 90.76% of Java online submissions for Array of Doubled Pairs.

Memory Usage: 50.1 MB, less than 81.79% of Java online submissions for Array of Doubled Pairs.

Next challenges:

Find Original Array From Doubled Array