[LeetCode 324] 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?

refer to some discussion post

use quickselect to find median, then use 

public class Solution {
    
    public int vi(int n, int original) {
        int virtual = (1+ 2 *original)%(n|1);
        return virtual;
    }
    public void wiggleSort(int[] nums) {
        int len = nums.length;
        int median = findMedian(nums);
        int i=0, j=0, k=nums.length-1;
        while(j<=k) {
            if(nums[vi(len,j)]>median) {
                swap(nums, vi(len,i++), vi(len,j++));
            }else if(nums[vi(len,j)]<median) {
                swap(nums, vi(len,k--), vi(len,j));
            }else{
                j++;
            }
        }
    }
    public int findMedian(int[] nums) {
        int len = nums.length;
        if(len%2 == 0) {
            return (findK(nums, len/2, 0, len-1) + findK(nums, len/2-1, 0, len-1))/2;
        }else {
            return findK(nums, len/2, 0, len-1);
        }
    }
    public int findK(int[] nums, int k, int s, int e) {
        if(s>=e) return nums[s];
        int m = partition(nums, s, e);
        if(m == k) return nums[m];
        else if(m<k) {
            return findK(nums, k, m+1, e);
        }else {
            return findK(nums, k, s, m-1);
        }
    }
    public int partition(int[] nums, int i, int j) {
        int pivot = nums[i];
        int m = i;
        int n = i+1;
        while(n<=j) {
            if(nums[n]<pivot){
                swap(nums, ++m, n);
            }
            n++;
        }
        swap(nums, i,m);
        return m;
    }
    public void swap(int[] nums, int a, int b) {
        int temp = nums[a];
        nums[a] = nums[b];
        nums[b] = temp;
    }
}