Kth Largest Element in an Array

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

For example,
Given [3,2,1,5,6,4] and k = 2, return 5.

 

public class Solution {
    public int findKthLargest(int[] nums, int k) {
        if (k < 1 || k > nums.length) {
        	return 0;
        }
        int[] kHeap = new int[k];
        for (int i = 0; i < k; i++) {
			heapInsert(kHeap, nums[i], i);
		}
        for (int i = k; i < nums.length; i++) {
			if (nums[i] > kHeap[0]) {
				kHeap[0] = nums[i];
				heapify(kHeap, 0, k);
			}
		}
		return kHeap[0];
    }

	private void heapify(int[] kHeap, int index, int heapSize) {
		// TODO Auto-generated method stub
		int left = index * 2 + 1;
		int right = index * 2 + 2;
		int little = index;
		while (left < heapSize) {
			if (kHeap[left] < kHeap[index]) {
				little = left;
			}
			if (right < heapSize && kHeap[right] < kHeap[little]) {
				little = right;
			}
			if (little != index) {
				swap(kHeap, little, index);
			} else {
				break;
			}
			index = little;
			left = index * 2 + 1;
			right = index * 2 + 2;
		}
	}

	private void heapInsert(int[] kHeap, int value, int index) {
		// TODO Auto-generated method stub
		kHeap[index] = value;
		while (index != 0) {
			int parent = (index - 1) / 2;
			if (kHeap[parent] > kHeap[index]) {
				swap(kHeap, parent, index);
				index = parent;
			} else {
				break;
			}
		}
	}

	private void swap(int[] arr, int i, int j) {
		// TODO Auto-generated method stub
		int tmp = arr[i];
		arr[i] = arr[j];
		arr[j] = tmp;
	}
}