| Question | 215. Kth Largest Element in an Array – Leetcode Javascript Solution |
| Difficulty | Medium |
| Question Type | Array |
| Question Link | https://leetcode.com/problems/kth-largest-element-in-an-array/ |
Problem Description :
Given an integer array nums and an integer k, return the kth largest element in the array. Note that it is the kth largest element in the sorted order, not the kth distinct element. You must solve it in O(n) time complexity.
Example 1:
Input: nums = [3,2,1,5,6,4], k = 2
Output: 5Example 2:
Input: nums = [3,2,3,1,2,4,5,5,6], k = 4
Output: 4
Constraints:
1 <= k <= nums.length <= 105
-104 <= nums[i] <= 104Solution 1 (Using Native Array Sort) :
var findKthLargest = function(nums, k) {
nums = nums.sort((a,b)=> a-b);
return nums[nums.length-k];
};Complexity Analysis :
Time complexity: O(n^2)
Space complexity: O(n)
Solution 2 ( Quicksort ) :
const findKthLargest = function(nums, k) {
const indexToFind = nums.length - k;
quickSort(nums, 0, nums.length-1);
return nums[indexToFind];
};
const quickSort = function(nums, left, right){
if(left < right){
const partitionIndex = getPartition(nums, left, right);
quickSort(nums, left, partitionIndex-1);
quickSort(nums, partitionIndex+1, right);
}
}
const getPartition = function(nums, left, right){
const pivotElement = nums[right];
let partitionIdx = left;
for(let j=left; j< right; j++){
if(nums[j] <= pivotElement){
swap(nums, partitionIdx, j);
partitionIdx++;
}
}
swap(nums, partitionIdx, right);
return partitionIdx;
}
const swap = function(nums, i, j){
const tmp = nums[i];
nums[i] = nums[j];
nums[j] = tmp;
}
// To run Program
const arr = [5, 3, 1, 6, 4, 2];
const kToFind = 2;
console.log(findKthLargest(arr, kToFind));Complexity Analysis :
Time complexity: O(nlogn)
Space complexity: O(n)
Solution 3 ( Quickselect ) ==> Optimized Solution
const findKthLargest = function(nums, k) {
const indexToFind = nums.length - k;
return quickSelect(nums, 0, nums.length-1, indexToFind);
};
const quickSelect = function(nums, left, right, indexToFind){
const partitionIndex = getPartition(nums, left, right);
if(partitionIndex === indexToFind){
return nums[partitionIndex];
}else if(indexToFind < partitionIndex){
return quickSelect(nums, left, partitionIndex-1, indexToFind);
}else{
return quickSelect(nums, partitionIndex+1, right, indexToFind);
}
}
const getPartition = function(nums, left, right){
let i = left;
for(let j=left; j<=right; j++){
if(nums[j] <= nums[right]){
swap(nums, i, j);
i++;
}
}
return i-1;
}
const swap = function(nums, i, j){
const tmp = nums[i];
nums[i] = nums[j];
nums[j] = tmp;
}
// To run Program
const arr = [5, 3, 1, 6, 4, 2];
const kToFind = 2;
console.log(findKthLargest(arr, kToFind));Complexity Analysis :
Time complexity: O(n)
Space complexity: O(n)
If you have any doubts, add in comment section. Will clarify at my level best. Also, if you have better solution, kindly share it, will grow together as to become better engineer.
