leetcode - Majority Element

Problem:
(1)Majority Element
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.

(2)Majority Element II
Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.

Solutions:
思路：
（1）用一个hashmap存储数字和count键值对，然后遍历该hashmap取出count>n/2（n/3）的数字。但是这样意味着两次遍历，耗时。
（2）用位运算：
java中，int是32bits来表示的，那么生成一个含有32位的list。对list中的每一位，遍历整个int数组，当该位出现次数多于一半的话，list中该位置1，然后将list中的32位转换成int。
（3）Moore’s Voting算法
每找出两个不同的element，就成对删除即count–，最终剩下的一定就是所求

下面展现(3)的代码

public class Solution {    int majorityElement(int[] nums) {        int elem = 0;        int count = 0;        for(int i = 0; i < num.size(); i++)  {            if(count == 0)  {                elem = num[i];                count = 1;            }            else    {                if(elem == num[i])                    count++;                else                    count--;            }        }        return elem;    }　　}