LeetCode 0707. Design Linked List Solution in Java, Python, C++, JavaScript, Go & Rust | Explanation + Code

Description

Design your implementation of the linked list. You can choose to use a singly or doubly linked list.
A node in a singly linked list should have two attributes: val and next. val is 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 the MyLinkedList class:

• MyLinkedList() Initializes the MyLinkedList object.
• int get(int index) Get the value of the indexth node in the linked list. If the index is invalid, return -1.
• void addAtHead(int 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.
• void addAtTail(int val) Append a node of value val as the last element of the linked list.
• void addAtIndex(int index, int val) Add a node of value val before the indexth node in the linked list. If index equals the length of the linked list, the node will be appended to the end of the linked list. If index is greater than the length, the node will not be inserted.
• void deleteAtIndex(int index) Delete the indexth node in the linked list, if the index is valid.

 

Example 1:

Input
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"]
[[], [1], [3], [1, 2], [1], [1], [1]]
Output
[null, null, null, null, 2, null, 3]

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

 

Constraints:

• 0 <= index, val <= 1000
• Please do not use the built-in LinkedList library.
• At most 2000 calls will be made to get, addAtHead, addAtTail, addAtIndex and deleteAtIndex.

Solutions

Solution 1

PythonJavaC++GoTypeScriptRust

class MyLinkedList: def __init__(self): self.dummy = ListNode() self.cnt = 0 def get(self, index: int) -> int: if index < 0 or index >= self.cnt: return -1 cur = self.dummy.next for _ in range(index): cur = cur.next return cur.val def addAtHead(self, val: int) -> None: self.addAtIndex(0, val) def addAtTail(self, val: int) -> None: self.addAtIndex(self.cnt, val) def addAtIndex(self, index: int, val: int) -> None: if index > self.cnt: return pre = self.dummy for _ in range(index): pre = pre.next pre.next = ListNode(val, pre.next) self.cnt += 1 def deleteAtIndex(self, index: int) -> None: if index >= self.cnt: return pre = self.dummy for _ in range(index): pre = pre.next t = pre.next pre.next = t.next t.next = None self.cnt -= 1 # Your MyLinkedList object will be instantiated and called as such: # obj = MyLinkedList() # param_1 = obj.get(index) # obj.addAtHead(val) # obj.addAtTail(val) # obj.addAtIndex(index,val) # obj.deleteAtIndex(index)(code-box)

class MyLinkedList { private ListNode dummy = new ListNode(); private int cnt; public MyLinkedList() { } public int get(int index) { if (index < 0 || index >= cnt) { return -1; } var cur = dummy.next; while (index-- > 0) { cur = cur.next; } return cur.val; } public void addAtHead(int val) { addAtIndex(0, val); } public void addAtTail(int val) { addAtIndex(cnt, val); } public void addAtIndex(int index, int val) { if (index > cnt) { return; } var pre = dummy; while (index-- > 0) { pre = pre.next; } pre.next = new ListNode(val, pre.next); ++cnt; } public void deleteAtIndex(int index) { if (index < 0 || index >= cnt) { return; } var pre = dummy; while (index-- > 0) { pre = pre.next; } var t = pre.next; pre.next = t.next; t.next = null; --cnt; } } /** * Your MyLinkedList object will be instantiated and called as such: * MyLinkedList obj = new MyLinkedList(); * int param_1 = obj.get(index); * obj.addAtHead(val); * obj.addAtTail(val); * obj.addAtIndex(index,val); * obj.deleteAtIndex(index); */(code-box)

class MyLinkedList { private: ListNode* dummy = new ListNode(); int cnt = 0; public: MyLinkedList() { } int get(int index) { if (index < 0 || index >= cnt) { return -1; } auto cur = dummy->next; while (index--) { cur = cur->next; } return cur->val; } void addAtHead(int val) { addAtIndex(0, val); } void addAtTail(int val) { addAtIndex(cnt, val); } void addAtIndex(int index, int val) { if (index > cnt) { return; } auto pre = dummy; while (index-- > 0) { pre = pre->next; } pre->next = new ListNode(val, pre->next); ++cnt; } void deleteAtIndex(int index) { if (index >= cnt) { return; } auto pre = dummy; while (index-- > 0) { pre = pre->next; } auto t = pre->next; pre->next = t->next; t->next = nullptr; --cnt; } }; /** * Your MyLinkedList object will be instantiated and called as such: * MyLinkedList* obj = new MyLinkedList(); * int param_1 = obj->get(index); * obj->addAtHead(val); * obj->addAtTail(val); * obj->addAtIndex(index,val); * obj->deleteAtIndex(index); */(code-box)

type MyLinkedList struct { dummy *ListNode cnt int } func Constructor() MyLinkedList { return MyLinkedList{&ListNode{}, 0} } func (this *MyLinkedList) Get(index int) int { if index < 0 || index >= this.cnt { return -1 } cur := this.dummy.Next for ; index > 0; index-- { cur = cur.Next } return cur.Val } func (this *MyLinkedList) AddAtHead(val int) { this.AddAtIndex(0, val) } func (this *MyLinkedList) AddAtTail(val int) { this.AddAtIndex(this.cnt, val) } func (this *MyLinkedList) AddAtIndex(index int, val int) { if index > this.cnt { return } pre := this.dummy for ; index > 0; index-- { pre = pre.Next } pre.Next = &ListNode{val, pre.Next} this.cnt++ } func (this *MyLinkedList) DeleteAtIndex(index int) { if index < 0 || index >= this.cnt { return } pre := this.dummy for ; index > 0; index-- { pre = pre.Next } t := pre.Next pre.Next = t.Next t.Next = nil this.cnt-- } /** * Your MyLinkedList object will be instantiated and called as such: * obj := Constructor(); * param_1 := obj.Get(index); * obj.AddAtHead(val); * obj.AddAtTail(val); * obj.AddAtIndex(index,val); * obj.DeleteAtIndex(index); */(code-box)

class LinkNode { public val: number; public next: LinkNode; constructor(val: number, next: LinkNode = null) { this.val = val; this.next = next; } } class MyLinkedList { public head: LinkNode; constructor() { this.head = null; } get(index: number): number { if (this.head == null) { return -1; } let cur = this.head; let idxCur = 0; while (idxCur < index) { if (cur.next == null) { return -1; } cur = cur.next; idxCur++; } return cur.val; } addAtHead(val: number): void { this.head = new LinkNode(val, this.head); } addAtTail(val: number): void { const newNode = new LinkNode(val); if (this.head == null) { this.head = newNode; return; } let cur = this.head; while (cur.next != null) { cur = cur.next; } cur.next = newNode; } addAtIndex(index: number, val: number): void { if (index <= 0) { return this.addAtHead(val); } const dummy = new LinkNode(0, this.head); let cur = dummy; let idxCur = 0; while (idxCur < index) { if (cur.next == null) { return; } cur = cur.next; idxCur++; } cur.next = new LinkNode(val, cur.next || null); } deleteAtIndex(index: number): void { if (index == 0) { this.head = (this.head || {}).next; return; } const dummy = new LinkNode(0, this.head); let cur = dummy; let idxCur = 0; while (idxCur < index) { if (cur.next == null) { return; } cur = cur.next; idxCur++; } cur.next = (cur.next || {}).next; } } /** * Your MyLinkedList object will be instantiated and called as such: * var obj = new MyLinkedList() * var param_1 = obj.get(index) * obj.addAtHead(val) * obj.addAtTail(val) * obj.addAtIndex(index,val) * obj.deleteAtIndex(index) */(code-box)

#[derive(Default)] struct MyLinkedList { head: Option<Box<ListNode>>, } /** * `&self` means the method takes an immutable reference. * If you need a mutable reference, change it to `&mut self` instead. */ impl MyLinkedList { fn new() -> Self { Default::default() } fn get(&self, mut index: i32) -> i32 { if self.head.is_none() { return -1; } let mut cur = self.head.as_ref().unwrap(); while index > 0 { match cur.next { None => { return -1; } Some(ref next) => { cur = next; index -= 1; } } } cur.val } fn add_at_head(&mut self, val: i32) { self.head = Some(Box::new(ListNode { val, next: self.head.take(), })); } fn add_at_tail(&mut self, val: i32) { let new_node = Some(Box::new(ListNode { val, next: None })); if self.head.is_none() { self.head = new_node; return; } let mut cur = self.head.as_mut().unwrap(); while let Some(ref mut next) = cur.next { cur = next; } cur.next = new_node; } fn add_at_index(&mut self, mut index: i32, val: i32) { let mut dummy = Box::new(ListNode { val: 0, next: self.head.take(), }); let mut cur = &mut dummy; while index > 0 { if cur.next.is_none() { return; } cur = cur.next.as_mut().unwrap(); index -= 1; } cur.next = Some(Box::new(ListNode { val, next: cur.next.take(), })); self.head = dummy.next; } fn delete_at_index(&mut self, mut index: i32) { let mut dummy = Box::new(ListNode { val: 0, next: self.head.take(), }); let mut cur = &mut dummy; while index > 0 { if let Some(ref mut next) = cur.next { cur = next; } index -= 1; } cur.next = cur.next.take().and_then(|n| n.next); self.head = dummy.next; } }(code-box)

Solution 2

PythonJavaC++GoTypeScript

class MyLinkedList: def __init__(self): self.e = [0] * 1010 self.ne = [0] * 1010 self.idx = 0 self.head = -1 self.cnt = 0 def get(self, index: int) -> int: if index < 0 or index >= self.cnt: return -1 i = self.head for _ in range(index): i = self.ne[i] return self.e[i] def addAtHead(self, val: int) -> None: self.e[self.idx] = val self.ne[self.idx] = self.head self.head = self.idx self.idx += 1 self.cnt += 1 def addAtTail(self, val: int) -> None: self.addAtIndex(self.cnt, val) def addAtIndex(self, index: int, val: int) -> None: if index > self.cnt: return if index <= 0: self.addAtHead(val) return i = self.head for _ in range(index - 1): i = self.ne[i] self.e[self.idx] = val self.ne[self.idx] = self.ne[i] self.ne[i] = self.idx self.idx += 1 self.cnt += 1 def deleteAtIndex(self, index: int) -> None: if index < 0 or index >= self.cnt: return -1 self.cnt -= 1 if index == 0: self.head = self.ne[self.head] return i = self.head for _ in range(index - 1): i = self.ne[i] self.ne[i] = self.ne[self.ne[i]] # Your MyLinkedList object will be instantiated and called as such: # obj = MyLinkedList() # param_1 = obj.get(index) # obj.addAtHead(val) # obj.addAtTail(val) # obj.addAtIndex(index,val) # obj.deleteAtIndex(index)(code-box)

class MyLinkedList { private int[] e = new int[1010]; private int[] ne = new int[1010]; private int head = -1; private int idx; private int cnt; public MyLinkedList() { } public int get(int index) { if (index < 0 || index >= cnt) { return -1; } int i = head; while (index-- > 0) { i = ne[i]; } return e[i]; } public void addAtHead(int val) { e[idx] = val; ne[idx] = head; head = idx++; ++cnt; } public void addAtTail(int val) { addAtIndex(cnt, val); } public void addAtIndex(int index, int val) { if (index > cnt) { return; } if (index <= 0) { addAtHead(val); return; } int i = head; while (--index > 0) { i = ne[i]; } e[idx] = val; ne[idx] = ne[i]; ne[i] = idx++; ++cnt; } public void deleteAtIndex(int index) { if (index < 0 || index >= cnt) { return; } --cnt; if (index == 0) { head = ne[head]; return; } int i = head; while (--index > 0) { i = ne[i]; } ne[i] = ne[ne[i]]; } } /** * Your MyLinkedList object will be instantiated and called as such: * MyLinkedList obj = new MyLinkedList(); * int param_1 = obj.get(index); * obj.addAtHead(val); * obj.addAtTail(val); * obj.addAtIndex(index,val); * obj.deleteAtIndex(index); */(code-box)

class MyLinkedList { private: int e[1010], ne[1010]; int head = -1, idx = 0, cnt = 0; public: MyLinkedList() { } int get(int index) { if (index < 0 || index >= cnt) { return -1; } int i = head; while (index--) { i = ne[i]; } return e[i]; } void addAtHead(int val) { e[idx] = val; ne[idx] = head; head = idx++; ++cnt; } void addAtTail(int val) { addAtIndex(cnt, val); } void addAtIndex(int index, int val) { if (index > cnt) { return; } if (index <= 0) { addAtHead(val); return; } int i = head; while (--index) { i = ne[i]; } e[idx] = val; ne[idx] = ne[i]; ne[i] = idx++; ++cnt; } void deleteAtIndex(int index) { if (index < 0 || index >= cnt) { return; } --cnt; if (index == 0) { head = ne[head]; return; } int i = head; while (--index) { i = ne[i]; } ne[i] = ne[ne[i]]; } }; /** * Your MyLinkedList object will be instantiated and called as such: * MyLinkedList* obj = new MyLinkedList(); * int param_1 = obj->get(index); * obj->addAtHead(val); * obj->addAtTail(val); * obj->addAtIndex(index,val); * obj->deleteAtIndex(index); */(code-box)

type MyLinkedList struct { e []int ne []int idx int head int cnt int } func Constructor() MyLinkedList { e := make([]int, 1010) ne := make([]int, 1010) return MyLinkedList{e, ne, 0, -1, 0} } func (this *MyLinkedList) Get(index int) int { if index < 0 || index >= this.cnt { return -1 } i := this.head for ; index > 0; index-- { i = this.ne[i] } return this.e[i] } func (this *MyLinkedList) AddAtHead(val int) { this.e[this.idx] = val this.ne[this.idx] = this.head this.head = this.idx this.idx++ this.cnt++ } func (this *MyLinkedList) AddAtTail(val int) { this.AddAtIndex(this.cnt, val) } func (this *MyLinkedList) AddAtIndex(index int, val int) { if index > this.cnt { return } if index <= 0 { this.AddAtHead(val) return } i := this.head for ; index > 1; index-- { i = this.ne[i] } this.e[this.idx] = val this.ne[this.idx] = this.ne[i] this.ne[i] = this.idx this.idx++ this.cnt++ } func (this *MyLinkedList) DeleteAtIndex(index int) { if index < 0 || index >= this.cnt { return } this.cnt-- if index == 0 { this.head = this.ne[this.head] return } i := this.head for ; index > 1; index-- { i = this.ne[i] } this.ne[i] = this.ne[this.ne[i]] } /** * Your MyLinkedList object will be instantiated and called as such: * obj := Constructor(); * param_1 := obj.Get(index); * obj.AddAtHead(val); * obj.AddAtTail(val); * obj.AddAtIndex(index,val); * obj.DeleteAtIndex(index); */(code-box)

class MyLinkedList { e: Array<number>; ne: Array<number>; idx: number; head: number; cnt: number; constructor() { this.e = new Array(1010).fill(0); this.ne = new Array(1010).fill(0); this.head = -1; this.idx = 0; this.cnt = 0; } get(index: number): number { if (index < 0 || index >= this.cnt) { return -1; } let i = this.head; while (index--) { i = this.ne[i]; } return this.e[i]; } addAtHead(val: number): void { this.e[this.idx] = val; this.ne[this.idx] = this.head; this.head = this.idx++; this.cnt++; } addAtTail(val: number): void { this.addAtIndex(this.cnt, val); } addAtIndex(index: number, val: number): void { if (index > this.cnt) { return; } if (index <= 0) { this.addAtHead(val); return; } let i = this.head; while (--index) { i = this.ne[i]; } this.e[this.idx] = val; this.ne[this.idx] = this.ne[i]; this.ne[i] = this.idx++; this.cnt++; } deleteAtIndex(index: number): void { if (index < 0 || index >= this.cnt) { return; } this.cnt--; if (index == 0) { this.head = this.ne[this.head]; return; } let i = this.head; while (--index) { i = this.ne[i]; } this.ne[i] = this.ne[this.ne[i]]; } } /** * Your MyLinkedList object will be instantiated and called as such: * var obj = new MyLinkedList() * var param_1 = obj.get(index) * obj.addAtHead(val) * obj.addAtTail(val) * obj.addAtIndex(index,val) * obj.deleteAtIndex(index) */(code-box)