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.

Example 1:

Input: [3,2,1,5,6,4] and k = 2
Output: 5

Example 2:

Input: [3,2,3,1,2,4,5,5,6] and k = 4
Output: 4

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

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class Solution { public: int findKthLargest(vector<int>& nums, int k) { priority_queue<int> pq; for(auto n:nums){ pq.push(-n); if(pq.size()>k) pq.pop(); } return -pq.top(); } }; class Solution_QS { int partition(vector<int>& nums, int l, int h){ int pivot = nums[h]; int i = l-1; for(int j=l; j<h; ++j){ if(nums[j]<=pivot){ swap(nums[++i], nums[j]); } } swap(nums[++i], nums[h]); return i; } int select(vector<int>& nums, int l, int h, int k){ if(l>h) return 0; int p = partition(nums, l, h); if(p==k) return nums[p]; if(p<k) return select(nums, p+1, h, k); else return select(nums, l, p-1, k); } public: int findKthLargest(vector<int>& nums, int k) { int n = nums.size(); k = n-k;//invert to incremental order return select(nums, 0, nums.size()-1, k); } };

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//Java, Quick Sort class Solution { void swap(int[] nums, int i, int j){ int tmp = nums[i]; nums[i] = nums[j]; nums[j] = tmp; } int partition(int[] nums, int l, int r){ int pivot = nums[r]; int i = l; for(int j=l; j<r; ++j){ if(nums[j]<=pivot){ swap(nums, i, j); i++; } } swap(nums, i, r); return i; } int select(int[] nums, int l, int r, int k){ if(l>r) return 0; int p = partition(nums, l, r); if(p==k) return nums[p]; if(p<k) return select(nums, p+1, r, k); else return select(nums, l, p-1, k); } public int findKthLargest(int[] nums, int k) { return select(nums, 0, nums.length-1, nums.length-k); } }