169. Majority Element

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.


题目大意：
给定一个长度为n的数组，寻找其中的“众数”。众数是指出现次数大于 ⌊ n/2 ⌋ 的元素。

你可以假设数组是非空的并且数组中的众数永远存在。

解答

• 此想法
  循环嵌套 nums.count(x) 时间复杂度过高

class Solution(object):
    def majorityElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        for x in nums:
            if nums.count(x) > len(nums)/2:
                return x
        

• 考虑 二分 set等方式

class Solution(object):
    def majorityElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        length = len(nums)/2
        listelement = set(nums)
        for x in listelement:
            if nums.count(x) > length:
                return x

写的很粗糙，这个link比较分明

http://bookshadow.com/weblog/2014/12/22/leetcode-majority-element

https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_majority_vote_algorithm
http://www.cs.utexas.edu/~moore/best-ideas/mjrty/index.html