LeetCode-in-All

169. Majority Element

Easy

Given an array nums of size n, return the majority element.

The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array.

Example 1:

Input: nums = [3,2,3]

Output: 3

Example 2:

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

Output: 2

Constraints:

• n == nums.length
• 1 <= n <= 5 * 104
• -109 <= nums[i] <= 109

Follow-up: Could you solve the problem in linear time and in O(1) space?

Solution

defmodule Solution do
  @spec majority_element(nums :: [integer]) :: integer
  def majority_element([head | tail]), do: recur(tail, 1, head)

  defp recur([head | tail], 0, _candidate), do: recur(tail, 1, head)

  defp recur([last], _count, candidate) when last === candidate, do: candidate

  defp recur([last, last], _count, candidate) when last === candidate, do: candidate

  defp recur([head | tail], count, candidate) when head === candidate,
    do: recur(tail, count + 1, candidate)

  defp recur([_head | tail], count, candidate), do: recur(tail, count - 1, candidate)

  defp recur([], _count, candidate), do: candidate
end

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