[LeetCode 215] Kth Largest Element in an Array

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.

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.

Solution:

Introduction to Algorithm, there was one step in quickselect — partition,

public int findKthLargest(int[] nums, int k) {return findK(nums, nums.length-k, 0, nums.length-1);}public int findK(int[] nums, int k, int s, int e) {if(s>=e) return nums[s];int m = partition(nums, s, e);if(m == k) return nums[m];else if(m<k) {return findK(nums, k, m+1, e);}else {return findK(nums, k, s, m-1);}}public int partition(int[] nums, int i, int j) {int pivot = nums[i];int m = i;int n = i+1;while(n<=j) {if(nums[n]<pivot){swap(nums, ++m, n);}n++;}swap(nums, i,m);return m;}public void swap(int[] nums, int a, int b) {int temp = nums[a];nums[a] = nums[b];nums[b] = temp;}

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