[Swift]LeetCode707. 设计链表 | Design Linked List

it2022-05-06  0

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Design your implementation of the linked list. You can choose to use the singly linked list or the doubly linked list. A node in a singly linked list should have two attributes: val and next. valis the value of the current node, and next is a pointer/reference to the next node. If you want to use the doubly linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.

Implement these functions in your linked list class:

get(index) : Get the value of the index-th node in the linked list. If the index is invalid, return -1.addAtHead(val) : Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.addAtTail(val) : Append a node of value val to the last element of the linked list.addAtIndex(index, val) : Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted.deleteAtIndex(index) : Delete the index-th node in the linked list, if the index is valid.

Example:

MyLinkedList linkedList = new MyLinkedList(); linkedList.addAtHead(1); linkedList.addAtTail(3); linkedList.addAtIndex(1, 2); // linked list becomes 1->2->3 linkedList.get(1); // returns 2 linkedList.deleteAtIndex(1); // now the linked list is 1->3 linkedList.get(1);    // returns 3

Note:

All values will be in the range of [1, 1000].The number of operations will be in the range of [1, 1000].Please do not use the built-in LinkedList library.

设计链表的实现。您可以选择使用单链表或双链表。单链表中的节点应该具有两个属性:val 和 next。val 是当前节点的值,next 是指向下一个节点的指针/引用。如果要使用双向链表,则还需要一个属性 prev 以指示链表中的上一个节点。假设链表中的所有节点都是 0-index 的。

在链表类中实现这些功能:

get(index):获取链表中第 index 个节点的值。如果索引无效,则返回-1。addAtHead(val):在链表的第一个元素之前添加一个值为 val 的节点。插入后,新节点将成为链表的第一个节点。addAtTail(val):将值为 val 的节点追加到链表的最后一个元素。addAtIndex(index,val):在链表中的第 index 个节点之前添加值为 val  的节点。如果 index 等于链表的长度,则该节点将附加到链表的末尾。如果 index 大于链表长度,则不会插入节点。deleteAtIndex(index):如果索引 index 有效,则删除链表中的第 index 个节点。

示例:

MyLinkedList linkedList = new MyLinkedList(); linkedList.addAtHead(1); linkedList.addAtTail(3); linkedList.addAtIndex(1,2); //链表变为1-> 2-> 3 linkedList.get(1); //返回2 linkedList.deleteAtIndex(1); //现在链表是1-> 3 linkedList.get(1); //返回3

提示:

所有值都在 [1, 1000] 之内。操作次数将在  [1, 1000] 之内。请不要使用内置的 LinkedList 库。
Runtime: 168 ms Memory Usage: 19.3 MB 1 class MyLinkedList { 2 var list:[Int] = [Int].init() 3 /** Initialize your data structure here. */ 4 init() { 5 6 } 7 8 /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */ 9 func get(_ index: Int) -> Int { 10 if list.count > index { 11 return list[index] 12 } 13 return -1 14 } 15 16 /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */ 17 func addAtHead(_ val: Int) { 18 if list.count > 0 { 19 list.insert(val,at:0) 20 } else { 21 list.append(val) 22 } 23 } 24 25 /** Append a node of value val to the last element of the linked list. */ 26 func addAtTail(_ val: Int) { 27 list.append(val) 28 } 29 30 /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */ 31 func addAtIndex(_ index: Int, _ val: Int) { 32 if list.count > index { 33 list.insert(val,at:index) 34 } else if list.count == index { 35 list.append(val) 36 } 37 } 38 39 /** Delete the index-th node in the linked list, if the index is valid. */ 40 func deleteAtIndex(_ index: Int) { 41 if list.count > index { 42 list.remove(at:index) 43 } 44 } 45 } 46 47 /** 48 * Your MyLinkedList object will be instantiated and called as such: 49 * let obj = MyLinkedList() 50 * let ret_1: Int = obj.get(index) 51 * obj.addAtHead(val) 52 * obj.addAtTail(val) 53 * obj.addAtIndex(index, val) 54 * obj.deleteAtIndex(index) 55 */

196ms

1 class MyLinkedList { 2 3 var list = [Int]() 4 5 /** Initialize your data structure here. */ 6 init() { 7 8 } 9 10 /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */ 11 func get(_ index: Int) -> Int { 12 if index < list.count { 13 return list[index] 14 } 15 16 return -1 17 } 18 19 /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */ 20 func addAtHead(_ val: Int) { 21 list.insert(val, at: 0) 22 } 23 24 /** Append a node of value val to the last element of the linked list. */ 25 func addAtTail(_ val: Int) { 26 list.append(val) 27 } 28 29 /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */ 30 func addAtIndex(_ index: Int, _ val: Int) { 31 if index <= list.count { 32 list.insert(val, at: index) 33 } 34 } 35 36 /** Delete the index-th node in the linked list, if the index is valid. */ 37 func deleteAtIndex(_ index: Int) { 38 if index < list.count { 39 list.remove(at: index) 40 } 41 } 42 }

216ms

1 class MyLinkedList { 2 3 private var count: Int = 0 4 private var head: Node? = nil 5 private var tail: Node? = nil 6 7 init() { 8 9 } 10 11 public func get(_ index: Int) -> Int { 12 return _get(index)?.val ?? -1 13 } 14 15 private func _get(_ index: Int) -> Node? { 16 var curr = head 17 18 for _ in 0..<index { 19 curr = curr?.next 20 } 21 22 return curr 23 } 24 25 public func addAtHead(_ val: Int) { 26 let node = Node() 27 node.val = val 28 29 if head == nil { 30 head = node 31 tail = node 32 } else { 33 node.next = head 34 head?.prev = node 35 head? = node 36 } 37 38 count += 1 39 } 40 41 public func addAtTail(_ val: Int) { 42 let node = Node() 43 node.val = val 44 45 if head == nil { 46 head = node 47 tail = node 48 } else { 49 node.prev = tail 50 tail?.next = node 51 tail = node 52 } 53 54 count += 1 55 } 56 57 public func addAtIndex(_ index: Int, _ val: Int) { 58 guard index <= count else { return } 59 if index == 0 { 60 addAtHead(val) 61 } else if index >= count { 62 addAtTail(val) 63 } else { 64 let node = _get(index - 1) 65 let new = Node() 66 new.val = val 67 68 new.next = node?.next 69 new.next?.prev = new 70 new.prev = node 71 node?.next = new 72 73 count += 1 74 } 75 } 76 77 public func deleteAtIndex(_ index: Int) { 78 guard index < count else { return } 79 if index == 0 { 80 let node = head! 81 if tail === node { 82 tail = nil 83 } 84 head = node.next 85 head?.prev = nil 86 node.next = nil 87 } else if index >= count - 1 { 88 let node = tail! 89 tail = tail?.prev 90 tail?.next = nil 91 node.prev = nil 92 } else { 93 let node = _get(index) 94 node?.prev?.next = node?.next 95 node?.next?.prev = node?.prev 96 } 97 count -= 1 98 } 99 100 private class Node { 101 var val: Int = 0 102 var next: Node? = nil 103 var prev: Node? = nil 104 } 105 }

224ms

1 class MyLinkedList { 2 3 private class Node { 4 var next: Node? 5 var prev: Node? 6 var val: Int 7 8 init(_ val: Int, next: Node? = nil, prev: Node? = nil) { 9 self.val = val 10 self.next = next 11 self.prev = prev 12 } 13 } 14 15 private var head: Node? 16 private var tail: Node? 17 var count = 0 18 var isEmpty: Bool { 19 return count == 0 20 } 21 22 /** Initialize your data structure here. */ 23 init() { 24 25 } 26 27 /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */ 28 func get(_ index: Int) -> Int { 29 guard index >= 0, index < self.count else {return -1} 30 return getNodeForIndex(index).val 31 } 32 33 /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */ 34 func addAtHead(_ val: Int) { 35 guard let head = head else { 36 self.head = Node(val) 37 self.tail = self.head 38 self.count += 1 39 return 40 } 41 let newHead = Node(val, next: head, prev: nil) 42 head.prev = newHead 43 self.head = newHead 44 self.count += 1 45 } 46 47 /** Append a node of value val to the last element of the linked list. */ 48 func addAtTail(_ val: Int) { 49 guard let tail = tail else { 50 self.head = Node(val) 51 self.tail = self.head 52 self.count += 1 53 return 54 } 55 let newTail = Node(val, next: nil, prev: tail) 56 tail.next = newTail 57 self.tail = newTail 58 self.count += 1 59 } 60 61 /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */ 62 func addAtIndex(_ index: Int, _ val: Int) { 63 guard index >= 0, index <= self.count else { return } 64 guard index != 0 else { 65 addAtHead(val) 66 return 67 } 68 guard index != self.count else { 69 addAtTail(val) 70 return 71 } 72 let current = getNodeForIndex(index - 1) 73 let newNode = Node(val, next: current.next, prev: current) 74 current.next = newNode 75 newNode.next?.prev = newNode 76 self.count += 1 77 } 78 79 /** Delete the index-th node in the linked list, if the index is valid. */ 80 func deleteAtIndex(_ index: Int) { 81 guard index >= 0, index < self.count else { return } 82 guard self.count > 1 else { 83 self.head = nil 84 self.tail = nil 85 self.count -= 1 86 return 87 } 88 guard index != 0 else { 89 self.head = self.head?.next 90 self.head?.prev = nil 91 self.count -= 1 92 return 93 } 94 guard index != self.count - 1 else { 95 self.tail = self.tail?.prev 96 self.tail?.next = nil 97 self.count -= 1 98 return 99 } 100 let current = getNodeForIndex(index) 101 let prev = current.prev! 102 let next = current.next! 103 prev.next = next 104 next.prev = prev 105 self.count -= 1 106 } 107 108 private func getNodeForIndex(_ index: Int) -> Node { 109 if index < self.count / 2 { 110 var current = self.head! 111 for _ in 0..<index { 112 current = current.next! 113 } 114 return current 115 } else { 116 var current = self.tail! 117 var i = self.count - 1 118 while i > index { 119 current = current.prev! 120 i -= 1 121 } 122 return current 123 } 124 } 125 }

328ms

1 class MyLinkedList { 2 3 var head: ListNode? 4 var tail: ListNode? 5 var size: Int 6 7 init(){ 8 self.size = 0 9 } 10 11 func get(_ index: Int) -> Int { 12 13 if index >= size { 14 return -1; 15 } 16 17 var tempNode = head 18 var i = 0 19 while i < index { 20 tempNode = tempNode?.next 21 i += 1 22 } 23 24 return tempNode!.val 25 } 26 27 func addAtHead(_ val: Int){ 28 29 let node = ListNode(val) 30 node.next = head 31 head = node 32 33 if tail == nil { 34 tail = head 35 } 36 size += 1 37 } 38 39 func addAtTail(_ val: Int){ 40 let node = ListNode(val) 41 if let tail = tail { 42 tail.next = node 43 }else { 44 head = node 45 } 46 47 tail = node 48 size += 1 49 50 51 } 52 53 func addAtIndex(_ index:Int, _ val: Int){ 54 55 if (index > self.size){ 56 return 57 } 58 59 if(index == self.size){ 60 self.addAtTail(val) 61 return 62 } 63 64 if (index == 0) { 65 self.addAtTail(val) 66 return 67 } 68 69 70 //需要两个节点--插入位置的前结点,和插入位置的后(现)结点 71 //index 位置前面的结点 72 var tempNode = head 73 var i = 0 74 while i < index-1 { 75 tempNode = tempNode?.next 76 i += 1 77 } 78 79 let nextNode = tempNode?.next 80 81 let node = ListNode(val) 82 tempNode?.next = node 83 node.next = nextNode 84 85 size += 1 86 } 87 88 func deleteAtIndex(_ index:Int) { 89 90 if index >= size { 91 return; 92 } 93 94 if(index == 0){ 95 if(size == 1){ 96 size = 0 97 head = nil 98 tail = nil 99 } 100 head = head?.next 101 size -= 1 102 return; 103 } 104 105 var tempNode = head 106 107 for _ in 0..<index-1{ 108 tempNode = tempNode?.next 109 } 110 111 if index == size - 1{ 112 tail = tempNode 113 tail?.next = nil 114 size -= 1 115 return; 116 } 117 118 let nextNode = tempNode?.next?.next 119 tempNode?.next = nextNode 120 size -= 1 121 } 122 }

 

转载于:https://www.cnblogs.com/strengthen/p/10506371.html


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