Wiggle Sort II

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

Example:
(1) Given nums = [1, 5, 1, 1, 6, 4], one possible answer is [1, 4, 1, 5, 1, 6]. 
(2) Given nums = [1, 3, 2, 2, 3, 1], one possible answer is [2, 3, 1, 3, 1, 2].

Note:
You may assume all input has valid answer.

Follow Up:
Can you do it in O(n) time and/or in-place with O(1) extra space?

Analyse: space: O(n), time: O(nlogn). 

Runtime: 140ms

class Solution {
public:
    void wiggleSort(vector<int>& nums) {
        // the number with odd index should be larger than others
        // find the larger part of the array, then insert the smaller and larger part correspondingly
        vector<int> temp = nums;
        sort(temp.begin(), temp.end());
        
        int n = nums.size(), k = (n + 1) / 2;
        for(int i = 0; i < nums.size(); i++)
            nums[i] = i & 1 ? temp[--n] : temp[--k];
    }
};