https://leetcode.com/problems/majority-element/description/
Given an array nums of size n, return the majority element.
The majority element is the element that appears more than ⌊n / 2⌋ times.
You may assume that the majority element always exists in the array.
Input: nums = [3,2,3]
Output: 3
Input: nums = [2,2,1,1,1,2,2]
Output: 2
n == nums.length
1 <= n <= 5 * 104
-109 <= nums[i] <= 109
Could you solve the problem in linear time and in O(1) space?