[LintCode] 第K大元素 Kth Largest Element

在数组中找到第k大的元素。
样例
给出数组 [9,3,2,4,8]，第三大的元素是 4
给出数组 [1,2,3,4,5]，第一大的元素是 5，第二大的元素是 4，第三大的元素是 3，以此类推
挑战
要求时间复杂度为O(n)，空间复杂度为O(1)

Find K-th largest element in an array.
Example
In array [9,3,2,4,8], the 3rd largest element is 4.
In array [1,2,3,4,5], the 1st largest element is 5, 2nd largest element is 4, 3rd largest element is 3 and etc.

Challenge
O(n) time, O(1) extra memory.

时间复杂度O（nlogn）?

class Solution {
    /*
     * @param k : description of k
     * @param nums : array of nums
     * @return: description of return
     */
    public int kthLargestElement(int k, int[] nums) {
        if(null == nums ||k <= 0 || nums.length < k) return Integer.MIN_VALUE;
        kthMax(nums, 0, nums.length-1, k);
        return nums[k-1];
    }
    public void kthMax(int[] nums, int left, int right, int k) {
        int mid = partition(nums, left, right);
        if(mid == k-1) return;
        if(mid > k-1)
            kthMax(nums, left, mid-1, k);
        else
            kthMax(nums, mid+1, right, k);
    }
    public int partition(int[] nums, int left, int right) {
        int temp = nums[left];
        while(left < right) {
            while(left < right && nums[right] <= temp)
                right--;
            nums[left] = nums[right];
            while(left < right && nums[left] > temp)
                left++;
            nums[right] = nums[left];
        }
        nums[left] = temp;
        return left;
    }
};