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A2Z Sheet

155. Insert node before head in Doubly Linked List

Easy
Step 6: Learn LinkedList [Single LL, Double LL, Medium, Hard Problems]›Learn Doubly LinkedList

Insert node before head in Doubly Linked List

EasyFunction: insertNodeBeforeHeadInDoublyLinkedList()
ASCI Mission Breakdown • Simple as Hell
"Master Insert node before head in Doubly Linked List: Take `nums` (number[]), execute an optimal learn doubly linkedlist strategy, and return boolean with clean edge-case handling."
Real-World Metaphor:

Think of Insert node before head in Doubly Linked List as an everyday real-world challenge: you receive input data, inspect its elements in sequence without making unnecessary duplicate passes, and transform the collection to reach the exact target without wasting computer memory.

Interactive Visual WalkthroughLINKED-LIST
Step 1 / 3
StatusInitialized
ModeScanning
Evaluating

1. Initialize State for Insert node before head in Doubly Linked List

Load inputs and initialize algorithmic registers.

How to Think About This (Mental Model)

  1. Unpack the problem parameters (`nums` (number[])) and clarify what is given vs what must be returned.
  2. Identify the optimal data structure or pattern (e.g. pointers, hash map, or stack) to avoid redundant recalculations.
  3. Walk through state transitions, handle edge cases (empty collections, single items, negative numbers), and return the verified result.

### The Mission Welcome to **Insert node before head in Doubly Linked List**! In this challenge, your goal is to write a high-performance, clean solution in your chosen programming language. You are given `nums` (number[]). Your job is to process this input using optimal logic and return boolean. ### How to Approach It - Read through the inputs carefully and look for patterns. - Think about what state you need to track as you examine each element. - Strive for optimal time complexity and keep your code readable and structured.

Examples

Example 1
Input: nums = [1,2,3,4,5]
Output: true

Constraints

  • 1 <= nums.length <= 10^5
  • -10^9 <= nums[i] <= 10^9
Topic Tags:
Learn LinkedList [Single LL, Double LL, Medium, Hard Problems]Learn Doubly LinkedListinsertNodeBeforeHeadInDoublyLinkedList
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