Formatted question description: https://leetcode.ca/all/707.html

707. Design Linked List

Level

Medium

Description

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. 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 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:

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 linkedList = new MyLinkedList(); // Initialize empty LinkedList
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

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.

Solution

This solution uses the doubly linked list.

Create a class Node that has data fields int val that is the node’s value, Node prev that is the node’s previous node, and Node next that is the node’s next node.

In class MyLinkedList, there are three data fields, which are Node head that is the first node, Node tail that is the last node, and int size that is the number of nodes in the linked list.

For the constructor, initialize head and tail to null, and size to 0.

For get(index), if index >= size, then return -1. Otherwise, find the index-th node starting from head, and return the node’s value.

For addAtHead(val), create a new node with value val. If size == 0, set both head and tail to be the new node. Otherwise, update the nodes around head and assign the new node to head. Increase size by 1.

For addAtTail(val), create a new node with value val. If size == 0, set both head and tail to be the new node. Otherwise, update the nodes around tail and assign the new node to tail. Increase size by 1.

For addAtIndex(index, val), first check index. If index == 0, then call addAtHead(val). Else, if index == size, then call addAtTail(val). Else, create a new node with value val, find the index-th node starting from head, and insert the new node at position index, with the nodes around the position updated.

For deleteAtIndex(index, val), first check index. If index == 0, then delete the node at head with the nodes around head updated. Else, if index == size - 1, then delete the node at tail with the nodes around tail updated. Else, find the index-th node starting from head, and delete the node, with the nodes around the position updated.

public class Design_Linked_List {

    class MyLinkedList {
        class Node {
            public int val;
            public Node next;
            public Node(int val) { this.val = val; this.next = null; }
            public Node(int val, Node next) { this.val = val; this.next = next; }
        }

        private Node head;
        private Node tail;
        private int size;

        public MyLinkedList() {
            this.head = this.tail = null;
            this.size = 0;
        }

        private Node getNode(int index) {
            Node n = new Node(0, this.head);
            while (index-- >= 0) {
                n = n.next;
            }
            return n;
        }

        public int get(int index) {
            if (index < 0 || index >= size) return -1;
            return getNode(index).val;
        }

        public void addAtHead(int val) {
            this.head = new Node(val, this.head);
            if (this.size++ == 0)
                this.tail = this.head;
        }

        public void addAtTail(int val) {
            Node n = new Node(val);
            if (this.size++ == 0)
                this.head = this.tail = n;
            else
                this.tail = this.tail.next = n;
        }

        public void addAtIndex(int index, int val) {
            if (index < 0 || index > this.size) return;
            if (index == 0)  { this.addAtHead(val); return; }
            if (index == size) { this.addAtTail(val); return; }
            Node prev = this.getNode(index - 1);
            prev.next = new Node(val, prev.next);
            ++this.size;
        }

        public void deleteAtIndex(int index) {
            if (index < 0 || index >= this.size) return;
            Node prev = this.getNode(index - 1);
            prev.next = prev.next.next;
            if (index == 0) this.head = prev.next;
            if (index == this.size - 1) this.tail = prev;
            --this.size;
        }
    }
}

############

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);
 */

// OJ: https://leetcode.com/problems/design-linked-list/
// Time:
//     get: O(N)
//     addAtHead: O(1)
//     addAtTail: O(1)
//     addAtIndex: O(N)
//     deleteAtIndex: O(N)
// Space: O(1)
class MyListNode {
public:
    int val;
    MyListNode *next = NULL;
    MyListNode(int v): val(v) {}
};

class MyLinkedList {
private:
    MyListNode dummy = MyListNode(0), *tail = &dummy;
    int len = 0;
public:
    MyLinkedList() {}
    
    int get(int index) {
        if (index >= len) return -1;
        auto p = dummy.next;
        while (index--) p = p->next;
        return p->val;
    }
    
    void addAtHead(int val) {
        auto node = new MyListNode(val);
        node->next = dummy.next;
        dummy.next = node;
        if (tail == &dummy) tail = node;
        ++len;
    }
    
    void addAtTail(int val) {
        tail->next = new MyListNode(val);
        tail = tail->next;
        ++len;
    }
    
    void addAtIndex(int index, int val) {
        if (index > len) return;
        auto node = new MyListNode(val);
        if (index == len) {
            tail->next = node;
            tail = node;
        } else {
            auto p = &dummy;
            while (index--) p = p->next;
            node->next = p->next;
            p->next = node;
        }
        ++len;
    }
    
    void deleteAtIndex(int index) {
        if (index >= len) return;
        auto p = &dummy;
        while (index--) p = p->next;
        auto node = p->next;
        p->next = node->next;
        if (tail == node) tail = p;
        delete node;
        --len;
    }
};

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)

############

class ListNode:

	def __init__(self, val):
		self.val = val
		self.next = None


class MyLinkedList:

	def __init__(self):
		self.head = None
		self.size = 0

	def get(self, index: 'int') -> 'int':
		if index < 0 or index >= self.size or \
				self.head is None:
			return -1
		return self.findIndex(index).val

	def addAtHead(self, val: 'int') -> 'None':
		self.addAtIndex(0, val)

	def addAtTail(self, val: 'int') -> 'None':
		self.addAtIndex(self.size, val)

	def addAtIndex(self, index: 'int', val: 'int') -> 'None':
		if index > self.size:
			return -1
		elif index == 0:
			head = ListNode(val)
			head.next, self.head = self.head, head
		else:
			pre = self.findIndex(index - 1)
			cur = ListNode(val)
			cur.next, pre.next = pre.next, cur
		self.size += 1

	def deleteAtIndex(self, index: 'int') -> 'None':
		if index < 0 or index >= self.size:
			return -1
		cur = self.findIndex(index - 1)
		cur.next = cur.next.next
		self.size -= 1

	def findIndex(self, index: 'int') -> 'None':
		cur = self.head
		for _ in range(index):
			cur = cur.next
		return cur
# 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)

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);
 */

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)
 */

#[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;
    }
}


/**
 * Your MyLinkedList object will be instantiated and called as such:
 * let obj = MyLinkedList::new();
 * let ret_1: i32 = obj.get(index);
 * obj.add_at_head(val);
 * obj.add_at_tail(val);
 * obj.add_at_index(index, val);
 * obj.delete_at_index(index);
 */

707 - Design Linked List

707. Design Linked List

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707. Design Linked List

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Description

Solution

All Problems

All Solutions