Top k Largest Numbers

Given an integer array, find the top k largest numbers in it.

Example

Given [3,10,1000,-99,4,100] and k = 3.
Return [1000, 100, 10].

思路：由于需要按从大到小的顺序，因此直接用PriorityQueue即可，用Partition的方法的话还需要排序。直接用PriorityQueue 写的代码量少。

 class Solution {
     /*
      * @param nums an integer array
      * @param k an integer
      * @return the top k largest numbers in array
      */
     public int[] topk(int[] nums, int k) {
         if (nums == null || nums.length < k) {
             return null;
         }

         int[] result = new int[k];
         PriorityQueue<Integer> minHeap = new PriorityQueue<>();
         for (int i = 0; i < nums.length; i++) {
             if (minHeap.size() < k) {
                 minHeap.add(nums[i]);
             } else {
                 int temp = minHeap.poll();
                 minHeap.add(Math.max(temp, nums[i]));
             }
         }

         for (int i = k - 1; i >= 0; i--) {
             result[i] = minHeap.poll();
         }

         return result;
     }
 };