added Design LinkedList (medium)

Author: minhyeong-joe

Medium/DesignLinkedList/README.md

@@ -0,0 +1,40 @@
+
+# Design Linked List
+[Leetcode Link](https://leetcode.com/problems/design-linked-list/)
+
+## Problem:
+
+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
+```
+
+## Note:
+
+- `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`.

Medium/DesignLinkedList/solution.py

@@ -0,0 +1,132 @@
+class Node:
+ def __init__(self, val=None, prev=None, next=None):
+ self.val = val
+ self.prev = prev
+ self.next = next
+
+class MyLinkedList:
+ def __init__(self):
+ """
+ Initialize your data structure here.
+ """
+ self.head = None
+ self.tail = None
+ self.length = 0
+
+ 
+
+ def get(self, index: int) -> int:
+ """
+ Get the value of the index-th node in the linked list. If the index is invalid, return -1.
+ """
+ if index < 0:
+ return -1
+ it = self.head
+ for i in range(index):
+ it = it.next
+ if it is None:
+ return -1
+ return it.val
+
+ 
+
+ def addAtHead(self, val: int) -> None:
+ """
+ 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.
+ """
+ if self.head is not None:
+ temp = self.head
+ self.head = Node(val, next=temp)
+ temp.prev = self.head
+ else:
+ self.head = Node(val)
+ self.tail = self.head
+ self.length += 1
+ 
+
+ def addAtTail(self, val: int) -> None:
+ """
+ Append a node of value val to the last element of the linked list.
+ """
+ if self.tail is not None:
+ self.tail.next = Node(val, prev=self.tail)
+ self.tail = self.tail.next
+ else:
+ self.tail = Node(val)
+ self.head = self.tail
+ self.length += 1
+ 
+
+ def addAtIndex(self, index: int, val: int) -> None:
+ """
+ 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.
+ """
+ if index > self.length:
+ return
+ if index == 0:
+ self.addAtHead(val)
+ return
+ if index == self.length:
+ self.addAtTail(val)
+ return
+ it = self.head
+ for i in range(index):
+ it = it.next
+ newNode = Node(val, prev=it.prev, next=it)
+ it.prev.next = newNode
+ it.prev = newNode
+ self.length += 1
+ 
+
+ def deleteAtIndex(self, index: int) -> None:
+ """
+ Delete the index-th node in the linked list, if the index is valid.
+ """
+ if index < 0 or index >= self.length:
+ return
+ if index == 0:
+ self.head = self.head.next
+ if self.head is not None:
+ self.head.prev = None
+ elif index == self.length-1:
+ self.tail = self.tail.prev
+ if self.tail is not None:
+ self.tail.next = None
+ else:
+ it = self.head
+ for i in range(index):
+ it = it.next
+ it.prev.next = it.next
+ it.next.prev = it.prev
+ self.length -= 1
+
+
+ def __str__(self):
+ output = ""
+ it = self.head
+ while it is not None:
+ output += str(it.val)
+ if it.next is not None:
+ output += " -> "
+ it = it.next
+ return output
+ 
+
+
+# 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)
+
+# test driver
+
+linkedList = MyLinkedList()
+linkedList.addAtHead(1)
+# linkedList.deleteAtIndex(0)
+print(linkedList)
+print("GET INDEX 2:", linkedList.get(0))
+print("GET HEAD:", str(linkedList.head.val))
+print("GET TAIL:", str(linkedList.tail.val))

README.md

@@ -76,6 +76,7 @@ Languages used: Java and Python
  - [Maximum Swap](Medium/MaximumSwap)
  - [Number of Operations to Make Network Connected](Medium/NumToMakeNetworkConnected)
  - [Sort Colors](Medium/SortColors)
+ - [Design Linked List](Medium/DesignLinkedList)
 - Hard
  - [Maximum Score Words Formed by Letters](Hard/MaximumScoreWords)
  - [Reducing Dishes](Hard/ReducingDishes)