What is the best way to find the majority element in an array?
The majority element appears more than half the time in an array. Finding it efficiently is a classic problem solved by Moore's Voting Algorithm.
Why Interviewers Ask This
This question tests knowledge of voting algorithms and frequency counting. Interviewers want to see if you can solve it in O(n) time and O(1) space. It also checks your ability to verify the candidate count after the initial pass.
How to Answer This Question
Start by explaining Moore's Voting Algorithm which maintains a candidate and a counter. Describe how to increment the counter for matching elements and decrement for mismatches. Explain what happens when the counter hits zero. Emphasize the need for a second pass to verify the candidate actually has the majority count.
Key Points to Cover
- Moore's Voting Algorithm
- Candidate and counter logic
- Verification pass required
- O(n) time, O(1) space
Sample Answer
I would use Moore's Voting Algorithm. I maintain a candidate variable and a counter. As I iterate, if the counter is zero, I pick the current element as the candidate. If the current element matches the candidate, I incr…
Common Mistakes to Avoid
- Skipping the verification step
- Assuming a majority always exists
- Using a hash map unnecessarily
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