Problem

Given an integer array nums that does not contain any zeros, find the largest positive integer k such that -k also exists in the array.

Return the positive integer k. If there is no such integer, return -1.

Example 1:

Input: nums = [-1,2,-3,3] Output: 3 Explanation: 3 is the only valid k we can find in the array.

Example 2:

Input: nums = [-1,10,6,7,-7,1] Output: 7 Explanation: Both 1 and 7 have their corresponding negative values in the array. 7 has a larger value.

Example 3:

Input: nums = [-10,8,6,7,-2,-3] Output: -1 Explanation: There is no a single valid k, we return -1.

Constraints:

1 <= nums.length <= 1000 -1000 <= nums[i] <= 1000 nums[i] != 0

Pre analysis

Will keep a hash and check if -k exists in hash, if yes, then compare with current max value and update it.

Post analysis

One can sort the array before checking, which will reduce the time complexity to O(nlogn) from O(n). Plus use two pointer approach to find the answer.