215. Kth Largest Element in an Array

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.

Example 1:

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

Example 2:

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

Constraints:

• 1 <= k <= nums.length <= 104
• 104 <= nums[i] <= 104

---

Solutions

Solution 1

Intuition

templates

void quick_sort(int q[], int l, int r)
{
    if (l >= r) return;

    int i = l - 1, j = r + 1, x = q[l + r >> 1];
    while (i < j)
    {
        do i ++ ; while (q[i] < x);
        do j -- ; while (q[j] > x);
        if (i < j) swap(q[i], q[j]);
    }
    quick_sort(q, l, j), quick_sort(q, j + 1, r);
}

private void quickSort(int[] nums, int l, int r) {
    if (l >= r) {
        return;
    }
    int i = l - 1, j = r + 1, x = nums[l + r >> 1];
    while (i < j) {
        do {
            i++;
        } while (nums[i] < x);
        do {
            j--;
        } while (nums[j] > x);
        if (i < j) {
            swap(nums, i, j);
        }
    }
    quickSort(nums, l, j);
    quickSort(nums, j + 1, r);

}

private void swap(int[] nums, int i, int j) {
    int temp = nums[i];
    nums[i] = nums[j];
    nums[j] = temp;
}

Code

class Solution {
    private int quickSort(int[] nums, int l, int r, int k) {
        if (l >= r) {
            return nums[l];
        }

        int i = l - 1, j = r + 1, x = nums[l + r >> 1];
        while (i < j) {
            do {
                i++;
            } while (nums[i] < x);
            do {
                j--;
            } while (nums[j] > x);
            if (i < j) {
                swap(nums, i, j);
            }
        }
        int s1 = j - l + 1 ;
        if (k <= s1) {
            return quickSort(nums, l, j, k);
        } else {
            return quickSort(nums, j + 1, r, k - s1);
        }
    }

    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }


    public int findKthLargest(int[] nums, int k) {
        return quickSort(nums, 0, nums.length-1, nums.length - k + 1);
    }
}

Complexity

• Time: O(nlogn)
• Space: O(logn)

---

Solution 2

Intuition

Code

Complexity

• Time:
• Space:

---