280. Wiggle Sort

Given an unsorted array nums, reorder it in-place such that nums[0] <= nums[1] >= nums[2] <= nums[3]....

Example:

Input: nums = [3,5,2,1,6,4]
Output: One possible answer is [3,5,1,6,2,4]

i代表在nums中的index，如果i是偶數，nums[i] <= nums[i - 1]，如果i是奇數，nums[i] >= nums[i - 1]。如果不符合這兩個規則，那就要調換數字。

void wiggleSort(vector<int>& nums) { // time: O(n); space: O(1)
    for (int i = 1; i < nums.size(); ++i) {
        if (i & 1) {
            if (nums[i] < nums[i - 1]) swap(nums[i], nums[i - 1]);
        } else {
            if (nums[i] > nums[i - 1]) swap(nums[i], nums[i - 1]);
        }
    }
}