Problem

Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.

You may assume that the array is non-empty and the majority element always exist in the array.

找到陣列中重複出現次數超過陣列長度⌊ n/2 ⌋ 的元素

Python 實現

# Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.
 

#
# You may assume that the array is non-empty and the majority element always exist in the array.

#author li.hzh
class Solution:
    def majorityElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        target = len(nums) // 2
        if target == 0:
            return
 
 nums[0]
        map = {}
        for val in nums:
            if val in map:
                map[val] += 1
                if map[val] > target:
                    return val
            else:
                map[val] = 1

    def majorityElement_sort(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
 

        nums.sort()
        return nums[len(nums)//2]

print(Solution().majorityElement_sort([8,8,7,7,7]))

分析

給出兩種方法，一種就是利用map儲存值及其對應出現的次數。最直接的想法了。

不過這道題，有個比較巧的思路。就是如果一個元素出現的次數超過一半，那麼排序後，[n/2]位的元素，一定是該元素。我覺得這個可能是出題者的意圖吧。於是有了解法二。