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.
在未排序的数组中找到第 k 个最大的元素。请注意，你需要找的是数组排序后的第 k 个最大的元素，而不是第 k 个不同的元素。
示例 1:
输入: [3,2,1,5,6,4] 和 k = 2
输出: 5
示例 2:
输入: [3,2,3,1,2,4,5,5,6] 和 k = 4
输出: 4
说明:
你可以假设 k 总是有效的，且 1 ≤ k ≤ 数组的长度。
24ms
1 class Solution { 2 func findKthLargest(_ nums: [Int], _ k: Int) -> Int { 3 return nums.sorted(by: >)[k - 1] 4 } 5 }
56ms
1 class Solution { 2 func findKthLargest(_ nums: [Int], _ k: Int) -> Int { 3 var newNums = nums 4 buildMaxHead(&newNums)//建最大堆 5 for i in ((newNums.count - k - 1)..<newNums.count).reversed() { 6 swap(&newNums, 0, i) 7 if i == newNums.count - k { 8 return newNums[i] 9 } 10 headify(&newNums, 0, i) 11 } 12 return 0 13 } 14 //MARK: 堆排序 15 func headSort(_ nums:inout [Int]) { 16 buildMaxHead(&nums) 17 for i in (1..<nums.count).reversed() { 18 swap(&nums, i, 0) 19 headify(&nums, 0, i) 20 } 21 } 22 //建最大堆 23 func buildMaxHead(_ nums:inout [Int]) { 24 for i in (0...nums.count/2).reversed() { 25 headify(&nums, i,nums.count) 26 } 27 } 28 //堆调整 29 func headify(_ nums:inout [Int], _ index: Int, _ length: Int) { 30 let leftChild = index * 2 + 1 // index节点的左孩子节点 31 let rightChild = index * 2 + 2 //index节点的右孩子节点 32 var largertIndex = index //节点与左右孩子的最大值 33 if leftChild < length && nums[leftChild] > nums[largertIndex] { 34 largertIndex = leftChild 35 } 36 if rightChild < length && nums[rightChild] > nums[largertIndex] { 37 largertIndex = rightChild 38 } 39 //如果交换了 40 if largertIndex != index { 41 swap(&nums, largertIndex, index)//交换节点值 42 headify(&nums, largertIndex,length)//调整变动的节点 43 } 44 } 45 func swap(_ nums:inout [Int],_ i:Int,_ j: Int) { 46 let temp = nums[i] 47 nums[i] = nums[j] 48 nums[j] = temp 49 } 50 }
56ms
1 class Solution { 2 func findKthLargest(_ nums: [Int], _ k: Int) -> Int { 3 var nums = nums 4 return find(&nums, 0, nums.count - 1, k) 5 } 6 7 func find(_ nums: inout [Int], _ start: Int, _ end: Int, _ k: Int) -> Int { 8 let pivot = partition(&nums, start, end) 9 let j = nums.count - pivot 10 if j > k { 11 return find(&nums, pivot + 1, end, k) 12 } 13 if j == k { 14 return nums[pivot] 15 } 16 return find(&nums, start, pivot - 1, k) 17 } 18 19 func partition(_ nums: inout [Int], _ start: Int, _ end: Int) -> Int { 20 guard start < end else { 21 return start 22 } 23 let pivot = Int.random(in: start...end) 24 nums.swapAt(pivot, end) 25 var index = start 26 for i in start..<end where nums[i] < nums[end] { 27 nums.swapAt(i, index) 28 index += 1 29 } 30 nums.swapAt(index, end) 31 return index 32 } 33 }
60ms
1 class Solution { 2 func findKthLargest(_ nums: [Int], _ k: Int) -> Int { 3 var arr = nums 4 return quickselect(arr: &arr, start: 0, end: arr.count - 1, k: arr.count - k) 5 } 6 7 private func quickselect(arr: inout[Int], start: Int, end: Int, k: Int) -> Int { 8 let pivot = partition(arr: &arr, start: start, end: end) 9 if pivot > k { return quickselect(arr: &arr, start: start, end: pivot - 1, k: k) } 10 if pivot == k { return arr[pivot] } 11 return quickselect(arr: &arr, start: pivot + 1, end: end, k: k) 12 } 13 14 private func partition(arr: inout[Int], start: Int, end: Int) -> Int { 15 guard start < end else { return start } 16 17 var i = start 18 let pivotIndex = Int.random(in: start ... end) 19 let pivot = arr[pivotIndex] 20 (arr[pivotIndex], arr[end]) = (arr[end], arr[pivotIndex]) 21 22 for j in start ..< end { 23 if arr[j] < pivot { 24 (arr[i], arr[j]) = (arr[j], arr[i]) 25 i += 1 26 } 27 } 28 29 (arr[i], arr[end]) = (arr[end], arr[i]) 30 return i 31 } 32 33 }
84ms
1 class Solution { 2 private var heapSize = 0 3 4 func findKthLargest(_ nums: [Int], _ k: Int) -> Int { 5 guard nums.count > 0 else { 6 return 0 7 } 8 var nums = nums 9 buildMaxHeap(&nums) 10 var i = 0 11 while i < k - 1 { 12 swap(&nums, 0, heapSize - 1) 13 heapSize -= 1 14 maxHeapAdjust(&nums, 0) 15 i += 1 16 } 17 return nums[0] 18 } 19 20 func buildMaxHeap(_ nums: inout [Int]) { 21 heapSize = nums.count 22 var i = heapSize >> 1 - 1 23 while i >= 0 { 24 maxHeapAdjust(&nums, i) 25 i -= 1 26 } 27 } 28 29 func maxHeapAdjust(_ nums: inout [Int],_ index: Int) { 30 var largest = index 31 var l = index << 1 + 1 32 var r = index << 1 + 2 33 if l < heapSize && nums[l] > nums[largest] { 34 largest = l 35 } 36 if r < heapSize && nums[r] > nums[largest] { 37 largest = r 38 } 39 if largest != index { 40 swap(&nums, largest, index) 41 maxHeapAdjust(&nums, largest) 42 } 43 } 44 45 func swap(_ nums: inout [Int], _ i: Int,_ j: Int) { 46 let temp = nums[i] 47 nums[i] = nums[j] 48 nums[j] = temp 49 } 50 }