Leetcode OJ 215. Kth largest Element in an Array sorting solution

Title Link: https://leetcode.com/problems/kth-largest-element-in-an-array/

215. Kth largest Element in an arraymy submissionsQuestionTotal Accepted: 43442 Total Submissions: 136063 Difficulty: Medium

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

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

Note:
You may assume k are always valid, 1≤k≤array ' s length.

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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Discuss

The element that is the K-large of the given array. If you sort first and then take the K element, then the time complexity is O (n*log N). With the data structure of the heap, the time complexity can be reduced to O (N*LOGK).

If you ask for a large element of K, then build a small top heap. For the small element K, then to build a big top heap! The heap of K-elements is constructed first, and the other i-k elements are compared with the top elements of the heap, and if they are smaller than the top elements of the heap, then the elements are included in the heap and the properties of the heap are maintained.

My AC Code

public class Kthlargestelementinanarray {public static void main (string[] args) {int[] a = {3, 2, 1, 5, 6, 4}; System.out.println (Findkthlargest (A, 1)); int[] B = { -1,2,0}; System.out.println (Findkthlargest (b, 3)); int[] c = {3,1,2,4}; System.out.println (Findkthlargest (c, 2));} public static int findkthlargest (int[] nums, int k) {int[] heap = new Int[k];heap[0] = nums[0];for (int i = 1; i < K; I + +) {Siftup (nums[i], heap, i);} for (int i = k; i < nums.length; i++) {Siftdown (nums, K, Heap, i);} return heap[0];} private static void Siftdown (int[] nums, int k, int[] heap, int i) {if (Nums[i] > Heap[0]) {heap[0] = Nums[i];int p = 0 ; while (P < k) {int minchild = 2 * p + 1;if (Minchild + 1 < k && Heap[minchild] > heap[minchild + 1]) Minch ILD ++;if (Minchild < K && Heap[p] > Heap[minchild]) {swap (heap, p, minchild);p = Minchild;} else break;}}} private static void Siftup (int num, int[] heap, int i) {int p = i;heap[i] = Num;while (P! = 0) {int parent = (p-1)/2if (Heap[parent] > Heap[p]) {swap (heap, p, parent);} p = parent;}} private static void Swap (int[] heap, int p, int parent) {int temp = heap[parent];heap[parent] = heap[p];heap[p] = temp;}}

Leetcode OJ 215. Kth largest Element in an Array sorting solution