Leetcode 215: Kth Largest Element in an Array, leetcodekth
Kth Largest Element in an ArrayTotal Accepted:3277Total Submissions:12235
FindKTh 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.
Note:
You may assume k is always valid, 1 ≤ k ≤ array's length.
[Idea]
In the algorithm book, a special section uses the same partition as quicksort. The algorithm complexity is O (n). The direct sort is O (n * log (n ))
[CODE]
public class Solution { //test case [2, 1], 1 public int findKthLargest(int[] nums, int k) { return findK(nums, nums.length-k, 0, nums.length-1); } private int findK(int[] nums, int k, int i, int j) { if(i>=j) return nums[i]; int m = partition(nums, i, j); if(m==k) return nums[m]; else if(m<k) { return findK(nums, k, m+1, j); } else { return findK(nums, k, i, m-1); } } private int partition(int[] nums, int i, int j) { int x = nums[i]; int m = i; int n = i+1; while(n<=j){ if(nums[n]<x) { swap(nums, ++m, n); } ++n; } swap(nums,i, m); return m; } private void swap(int[] nums, int i, int j) { int temp = nums[i]; nums[i] = nums[j]; nums[j] = temp; }}