Problem editorial

Majority Element II

MediumArray/Matrix Manipulation PatternsArrayCountingIteration

Majority Element II: the approach in brief

The problem

Implement the Solution class and its majorityElement method. The parameter nums is an array of integers, and n is the number of elements in nums.

Pattern

Majority Element II is a Array/Matrix Manipulation Patterns problem, in the Hashing - Frequency Map / Counting subpattern. The pattern covers in-place operations, hashing, prefix sums, spiral traversal, and cyclic sort

Approach outline

How many distinct values could possibly occur more than one-third of the time?
Keep track of only a small number of candidate values while scanning the array.
When the current value matches a candidate, increase that candidate's count; otherwise, consider how unmatched values can cancel candidate counts.

Complexity

The reference solution runs in O(n) time and O(1) space.

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Practise Majority Element II and the problems around it

Majority Element II is a Array/Matrix Manipulation Patterns problem, in the Hashing - Frequency Map / Counting subpattern. Once the approach above makes sense, write it yourself and then work through the neighbouring problems that reuse it.

Majority Element II