Majority Element Moore's Voting Algorithm in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Majority Element in an array?

The Majority Element is the element that appears more than half the times in the array (more than n/2 times).

intermediate

What is the main idea behind Moore's Voting Algorithm?

Moore's Voting Algorithm finds the majority element by maintaining a candidate and a count. It increases the count when the same element appears and decreases it when a different element appears, resetting the candidate when count reaches zero.

intermediate

Why does Moore's Voting Algorithm work for finding the majority element?

Because the majority element appears more than half the time, it will remain as the candidate after canceling out all other elements paired with it.

beginner

What are the two main steps in Moore's Voting Algorithm?

1. Find a candidate for majority element by counting and canceling out different elements.<br>2. Verify if the candidate is actually the majority by counting its occurrences.

beginner

What is the time complexity of Moore's Voting Algorithm?

The time complexity is O(n) because it scans the array twice: once to find the candidate and once to verify it.

What does Moore's Voting Algorithm use to keep track of the majority element candidate?

A A stack to store elements

B A hash map to count frequencies

C Sorting the array first

D A candidate variable and a count variable

Moore's Voting Algorithm maintains a candidate and a count to find the majority element efficiently.

What happens when the count reaches zero in Moore's Voting Algorithm?

A The algorithm stops

B The candidate is reset to the current element

C The count is doubled

D The candidate is removed permanently

When count reaches zero, the algorithm resets the candidate to the current element and count to 1.

Why do we need to verify the candidate after finding it in Moore's Voting Algorithm?

A Because verification improves time complexity

B Because the algorithm always finds the majority element without verification

C Because the candidate might not actually be the majority element

D Because verification sorts the array

Verification is needed to confirm the candidate appears more than n/2 times.

What is the space complexity of Moore's Voting Algorithm?

A O(1)

B O(n)

C O(log n)

D O(n^2)

Moore's Voting Algorithm uses constant extra space, only two variables.

If no element appears more than n/2 times, what will Moore's Voting Algorithm return?

A A candidate that is not a majority element

B No candidate

C An error

D The smallest element

The algorithm returns a candidate, but verification will show it is not a majority element.

Explain how Moore's Voting Algorithm finds the majority element in an array.

Think about how the algorithm cancels out different elements.

Describe why Moore's Voting Algorithm is efficient compared to counting frequencies with a hash map.

Focus on space and time usage differences.