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Problem

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

Approach 1: Hash Table

Algorithm

利用 hash map 紀錄每過數字出現的頻率, 遍歷 map 找到出現頻率最高的數字返回

Implementation

func majorityElement(nums []int) int {
	m := make(map[int]int)
	for i := 0; i < len(nums); i++ {
		m[nums[i]]++
	}
	var maxKey, maxVal int
	for k, v := range m {
		if v > maxVal {
			maxVal = v
			maxKey = k
		}
	}

	return maxKey
}

Complexity Analysis

• Time complexity: $O(n)$

  • Where n is the number of given array.
  • Runtime: 25 ms, faster than 75.69% of Go online submissions.

• Space complexity: $O(n)$

  • Where n is the number of given array.
  • Memory Usage: 6 MB, less than 99.31% of Go online submissions.