Median

Given a unsorted array with integers, find the median of it. 

A median is the middle number of the array after it is sorted. 

If there are even numbers in the array, return the N/2-th number after sorted.

Have you met this question in a real interview? 

Yes

Example

Given [4, 5, 1, 2, 3], return 3

Given [7, 9, 4, 5], return 5

Challenge

O(n) time.

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

        return quickSort(nums, 0, nums.length-1, (nums.length+1)/2);

    }

    

    private int quickSort(int[] nums, int i, int j, int k){

        int start = i++;

        while(i<=j){

            while(i <= j && nums[i] < nums[start]) i++;

            while(i <= j && nums[j] >= nums[start]) j--;

            if(i < j)

            swap(nums, i, j);

        }

        swap(nums, start, j);

        if(k == j + 1) return nums[j];

       

        else if(k > j + 1) return quickSort(nums, j+1, nums.length-1, k);

        else {

            return quickSort(nums, 0, j-1, k);

        }

    }

    private void swap(int[] nums, int i, int j){

        int temp = nums[i];

        nums[i] = nums[j];

        nums[j] = temp;

    }

}