Add Two Numbers
You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.
Why Interviewers Ask This
Cisco evaluates candidates on their ability to manipulate low-level data structures efficiently. This question tests logical precision in handling edge cases like carry propagation and unequal list lengths. It specifically assesses whether you can implement a linear time solution while maintaining code clarity, a critical skill for network infrastructure development where performance is paramount.
How to Answer This Question
Key Points to Cover
- Explicitly mentioning the use of a dummy head node to streamline pointer logic
- Correctly handling the carry propagation when the sum exceeds nine
- Accounting for lists of unequal lengths by treating missing nodes as zero
- Ensuring the loop continues until all nodes are processed AND no carry remains
- Stating the time complexity is linear relative to the longer input list
Sample Answer
Common Mistakes to Avoid
- Forgetting to check for a remaining carry after the main loop finishes, leading to missing the final digit
- Using complex conditional logic inside the loop instead of treating missing nodes as zero values
- Attempting to reverse the input lists before processing, which adds unnecessary O(N) overhead
- Failing to initialize the carry variable to zero, causing incorrect calculations from the start
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