Kth Largest Element in an Array

Kth Largest Element in an Array

问题：

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.

思路：

　　快速排序，最大堆

我的代码：

public class Solution {
    public int findKthLargest(int[] nums, int k) {
        return helper(nums, nums.length-k);
    }
    public int helper(int[]nums, int k)
    {
        int low = 0; 
        int high = nums.length-1;
        int key = nums[0];
        while(low < high)
        {
            while(low<high && nums[high]>=key) high--;
            nums[low] = nums[high];
            while(low<high && nums[low]<key) low++;
            nums[high] = nums[low];
        }
        nums[low] = key;
        if(low == k) return nums[low];
        return low < k ? helper(Arrays.copyOfRange(nums, low+1, nums.length), k-(low+1)) : helper(Arrays.copyOfRange(nums, 0, low), k);
    }
}

他人代码：

public int findKthLargest(int[] nums, int k) {
        PriorityQueue<Integer> queue = new PriorityQueue<Integer>(k,new Comparator<Integer>(){
            public int compare(Integer a, Integer b) {
                return a-b;
            }
        });
        for(int i=0;i<nums.length;i++) {
            if(queue.size()<k) queue.add(nums[i]);
            else {
                if(nums[i]>queue.peek()) {
                    queue.remove();
                    queue.add(nums[i]);
                }
            }
        }
        return queue.remove();
    }

学习之处：

• 比较常规的问题了，之前这个问题就知道两种思路，一种是快速排序的Partition，另外一种是最小堆，关键的地方在于实现Partition，java中如何调用最小堆。