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➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/10037429.html
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Sort a linked list in O(n log n) time using constant space complexity.
Example 1:
Input: 4->2->1->3 Output: 1->2->3->4
Example 2:
Input: -1->5->3->4->0 Output: -1->0->3->4->5
在 O(n log n) 时间复杂度和常数级空间复杂度下，对链表进行排序。
示例 1:
输入: 4->2->1->3 输出: 1->2->3->4
示例 2:
输入: -1->5->3->4->0 输出: -1->0->3->4->5
124ms
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * public var val: Int 5 * public var next: ListNode? 6 * public init(_ val: Int) { 7 * self.val = val 8 * self.next = nil 9 * } 10 * } 11 */ 12 class Solution { 13 func sortList(_ head: ListNode?) -> ListNode? { 14 var arr = [Int]() 15 var cur = head 16 17 while cur != nil { 18 arr.append(cur!.val) 19 cur = cur!.next 20 } 21 22 arr.sort() 23 24 if arr.count < 2 { 25 return head 26 } else { 27 28 var head = ListNode(arr[0]) 29 var curr: ListNode? = head 30 31 for i in 1..<arr.count { 32 curr?.next = ListNode(arr[i]) 33 curr = curr?.next 34 } 35 36 return head 37 } 38 } 39 }
128ms
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * public var val: Int 5 * public var next: ListNode? 6 * public init(_ val: Int) { 7 * self.val = val 8 * self.next = nil 9 * } 10 * } 11 */ 12 class Solution { 13 func sortList(_ head: ListNode?) -> ListNode? { 14 var nums = [Int]() 15 var node = head 16 17 while node != nil { 18 nums.append(node!.val) 19 node = node!.next 20 } 21 22 nums.sort() 23 24 var mockNode = ListNode(0) 25 node = mockNode 26 27 for num in nums { 28 node?.next = ListNode(num) 29 node = node?.next 30 } 31 32 return mockNode.next 33 34 } 35 }
220ms
1 extension ListNode { 2 func length() -> Int { 3 return 1 + (self.next?.length() ?? 0) 4 } 5 } 6 7 class Solution { 8 func sortList(_ head: ListNode?) -> ListNode? { 9 guard let head = head else { 10 return nil 11 } 12 return divideAndMerge(head, length: head.length()) 13 } 14 15 func divideAndMerge(_ head: ListNode?, length: Int) -> ListNode? { 16 guard length > 1 else { 17 return head 18 } 19 20 let mid: ListNode? = { 21 var current = head 22 var previous = head 23 for _ in 0..<length / 2 { 24 previous = current 25 current = current?.next 26 } 27 previous?.next = nil 28 return current 29 }() 30 31 let left = divideAndMerge(head, length: length / 2) 32 let right = divideAndMerge(mid, length: length - (length / 2)) 33 return merge(left, mid: right) 34 } 35 36 func merge(_ head: ListNode?, mid: ListNode?) -> ListNode? { 37 var head = head 38 var mid = mid 39 var mergedList: ListNode? 40 var endNode: ListNode? 41 42 while let headNode = head, let midNode = mid { 43 var currentNode: ListNode! 44 if headNode.val < midNode.val { 45 currentNode = headNode 46 head = headNode.next 47 headNode.next = nil 48 } else { 49 currentNode = midNode 50 mid = midNode.next 51 midNode.next = nil 52 } 53 if mergedList == nil { 54 endNode = currentNode 55 mergedList = currentNode 56 } else { 57 endNode?.next = currentNode 58 endNode = currentNode 59 } 60 } 61 if let headNode = head { 62 endNode?.next = headNode 63 } else { 64 endNode?.next = mid 65 } 66 return mergedList 67 } 68 }
268ms
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * public var val: Int 5 * public var next: ListNode? 6 * public init(_ val: Int) { 7 * self.val = val 8 * self.next = nil 9 * } 10 * } 11 */ 12 class Solution { 13 func sortList(_ head: ListNode?) -> ListNode? { 14 if head == nil || head?.next == nil { 15 return head 16 } 17 18 // split in half 19 var slow = head, fast = head?.next 20 while fast != nil && fast?.next != nil { 21 slow = slow?.next 22 fast = fast?.next?.next 23 } 24 25 // break the list 26 let secondHead = slow?.next 27 slow?.next = nil 28 var l1 = self.sortList(secondHead) 29 var l2 = self.sortList(head) 30 31 var resHead: ListNode? = nil 32 var resTail: ListNode? = nil 33 var next: ListNode? = nil 34 while let l1a = l1, let l2a = l2 { 35 if l1a.val < l2a.val { 36 next = l1 37 l1 = l1a.next 38 } else { 39 next = l2 40 l2 = l2a.next 41 } 42 43 resHead = resHead ?? next 44 resTail?.next = next 45 resTail = next 46 47 } 48 49 if l1 != nil { 50 resTail?.next = l1 51 } else if l2 != nil { 52 resTail?.next = l2 53 } 54 55 return resHead 56 } 57 }
296ms
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * public var val: Int 5 * public var next: ListNode? 6 * public init(_ val: Int) { 7 * self.val = val 8 * self.next = nil 9 * } 10 * } 11 */ 12 class Solution { 13 func sortList(_ head: ListNode?) -> ListNode? { 14 guard let head = head else{ 15 return nil 16 } 17 guard head.next != nil else{ 18 return head 19 } 20 var cur:ListNode? = head 21 var length = 0 22 while cur != nil{ 23 length += 1 24 cur = cur!.next 25 } 26 let dummy = ListNode(-1) 27 dummy.next = head 28 var left:ListNode? ,right:ListNode?,tail:ListNode? 29 var step = 1 30 while step < length{ 31 cur = dummy.next 32 tail = dummy 33 while(cur != nil){ 34 left = cur 35 right = split(left,step) 36 cur = split(right,step) 37 tail = merge(left,right,tail) 38 } 39 40 step = step << 1 41 } 42 return dummy.next 43 44 } 45 func split(_ head:ListNode? ,_ n:Int) -> ListNode?{ 46 guard let head = head else{ 47 return nil 48 } 49 var phead:ListNode? = head 50 for _ in 1..<n{ 51 if phead != nil{ 52 phead = phead!.next 53 } 54 } 55 if phead == nil{ 56 return nil 57 } 58 let secondNode = phead!.next 59 phead!.next = nil 60 return secondNode 61 } 62 func merge(_ l1:ListNode?, _ l2:ListNode?, _ head:ListNode?) -> ListNode?{ 63 var cur:ListNode? = head 64 var l1 = l1,l2 = l2 65 while l1 != nil && l2 != nil{ 66 if l1!.val > l2!.val{ 67 cur!.next = l2 68 cur = l2 69 l2 = l2!.next 70 }else{ 71 cur!.next = l1 72 cur = l1 73 l1 = l1!.next 74 } 75 } 76 cur!.next = l1 == nil ? l2 : l1 77 while(cur!.next != nil) { 78 cur = cur!.next 79 } 80 return cur 81 } 82 }
336ms
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * public var val: Int 5 * public var next: ListNode? 6 * public init(_ val: Int) { 7 * self.val = val 8 * self.next = nil 9 * } 10 * } 11 */ 12 class Solution { 13 func sortList(_ head: ListNode?) -> ListNode? { 14 if head == nil || head?.next == nil { return head } 15 16 let middle = findMiddle(head) 17 let l2 = sortList(middle?.next) 18 middle?.next = nil 19 let l1 = sortList(head) 20 return merge(l1, l2) 21 } 22 23 24 private func merge(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? { 25 var dummy = ListNode(0), tail = dummy 26 var l1 = l1, l2 = l2 27 28 while l1 != nil && l2 != nil { 29 if l1!.val < l2!.val { 30 tail.next = l1 31 l1 = l1?.next 32 }else { 33 tail.next = l2 34 l2 = l2?.next 35 } 36 tail = tail.next! 37 } 38 if l1 != nil { 39 tail.next = l1 40 }else if l2 != nil { 41 tail.next = l2 42 } 43 44 return dummy.next 45 } 46 47 48 private func findMiddle(_ head: ListNode?) -> ListNode? { 49 var slow = head, fast = head 50 while fast?.next != nil && fast?.next?.next != nil { 51 slow = slow?.next 52 fast = fast?.next?.next 53 } 54 return slow 55 } 56 }