Majority Element

问题描述：

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.

解决思路：这是一个求解数组主元素的题目，数组的主元素是指数组中出现次数超过一半的元素。此题是假设数组非空并且主元素存在，所以比较简单。主元素总会比其他元素多，我们设置两个变量maj_index用于记录主元素的位置，count用于记录主元素出现的次数，然后一次比较数组元素，如果相同则count加1，不同则减1，若count为零，则替换maj_index，并将count置为1.

C++:

class Solution {public:    int majorityElement(vector<int> &num) {        int maj_index,count;        maj_index = 0;        count = 1;        for(int i =1; i < num.size(); i++){            if (num[i] == num[maj_index])                count ++;            else                count --;            if (count == 0){                maj_index = i;                count = 1;            }        }        return num[maj_index];    }};

python:

class Solution:    # @param num, a list of integers    # @return an integer    def majorityElement(self, num):        maj_index = 0        count = 1        for i in range(1,len(num)):            if num[i] == num[maj_index]:                count += 1            else:                count -= 1            if count == 0:                maj_index = i                count = 1        return num[maj_index]

延伸阅读：http://www.geeksforgeeks.org/majority-element/