[lintcode]Kth Largest Element

Kth Largest Element

 

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.

Note

You can swap elements in the array

Challenge

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

 

class Solution {
    //param k : description of k
    //param numbers : array of numbers
    //return: description of return
    public int kthLargestElement(int k, ArrayList<Integer> numbers) {
        // write your code here
         int L = 0, R = numbers.size() - 1;
         while (L < R) {
             int left = L, right = R;
             int key = numbers.get(left);
             while (left < right) {
                 while (left<right &&numbers.get(right) < key) --right;
                 numbers.set(left,numbers.get(right));
                 while (left<right &&numbers.get(left)>= key) ++left;
                 numbers.set(right,numbers.get(left)); 
             }
             numbers.set(left,key);
             if (left == k - 1) return numbers.get(k-1);
             else if (left > k - 1) R = left - 1;
             else L = left + 1;
        }
        return numbers.get(k-1);
   }
};