Median

O(n) worst, O(nlogn) average. Use quickSort

This is quickSort

public class Solution {
    /**
     * @param nums: A list of integers.
     * @return: An integer denotes the middle number of the array.
     */
    public int median(int[] nums) {
        // write your code here
        if (nums == null || nums.length == 0) {
            return 0;
        }
        quickSort(nums, 0, nums.length - 1);
        return nums[(nums.length - 1) / 2];
    }
    
    private void quickSort(int[] nums, int start, int end) {
        if (start >= end) {
            return;
        }
        
        int left = start;
        int right = end;
        int pivot = nums[start + (end - start) / 2];
        while (left <= right) {
            while (left <= right && nums[left] < pivot) {
                left++;
            }
            while (left <= right && nums[right] > pivot) {
                right--;
            }
            if (left <= right) {
                int tmp = nums[left];
                nums[left] = nums[right];
                nums[right] = tmp;
                left++;
                right--;
            }
        }
        
        quickSort(nums, start, right);
        quickSort(nums, left, end);
    }
}