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
• -231 <= nums[i] <= 231 - 1

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

Solution

class Solution {
    func majorityElement(_ arr: [Int]) -> Int {
        var count = 1
        var majority = arr[0]

        // For Potential Majority Element
        for i in 1..<arr.count {
            if arr[i] == majority {
                count += 1
            } else {
                if count > 1 {
                    count -= 1
                } else {
                    majority = arr[i]
                }
            }
        }

        // For Confirmation
        count = 0
        for num in arr {
            if num == majority {
                count += 1
            }
        }
        return count >= (arr.count / 2) + 1 ? majority : -1
    }
}

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