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Find Majority Element (Boyer-Moore Algorithm)

Certification: Basic Level Accuracy: 70% Submissions: 10 Points: 8

Write a Java program to find the majority element in an array of integers using the Boyer-Moore Voting Algorithm.

Example 1
    

  • Input: nums = [3,2,3]
    • 

  • Output: 3
    • 

  • Explanation:

      

    • 3 appears 2 times → majority of 3 elements
      • 

    

    •
Example 2
    

  • Input: nums = [2,2,1,1,1,2,2]
    • 

  • Output: 2
    • 

  • Explanation:

      

    • 2 appears 4 times → majority of 7 elements
      • 

    

    •
Constraints
    

  • 1 ≤ nums.length ≤ 5 * 10^4
    • 

  • -10^9 ≤ nums[i] ≤ 10^9
    • 

  • A majority element is guaranteed
    • 

  • Time Complexity: O(n)
    • 

  • Space Complexity: O(1)
    •
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Hint
Solution

Solution Hints

    
  
  • Use the Boyer-Moore Voting Algorithm which works in two passes.
    • 
  
  • First pass establishes a candidate for the majority element.
    • 
  
  • Second pass verifies if the candidate is actually the majority element.
    • 
  
  • The algorithm is optimal in terms of both time and space complexity.
    • 
  
  • No need for additional data structures like HashMap.
    •

Steps to solve by this approach:

 Step 1: Initialize count to 0 and candidate to null.

 Step 2: Iterate through the array. If count is 0, set the current element as the candidate.

 Step 3: If the current element equals the candidate, increment count; otherwise, decrement count.

 Step 4: After the first pass, we have a candidate for the majority element.

 Step 5: Verify the candidate is indeed the majority element by counting its occurrences.

 Step 6: If the count is greater than n/2, return the candidate; otherwise, return -1.

 Step 7: Since the problem states there's always a majority element, we'll always return the candidate from step 4.

Submitted Code :