題目描述：
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.

找到這個陣列中出現次數超過n/2次的元素，假設這個元素一定是存在的。
一個簡單的方法就是排序後找中間的元素，程式碼如下：

class
 
 Solution {
public:
    int majorityElement(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        return nums[nums.size() / 2];
    }

};

還有一種方法就是分而治之，每次將這個陣列分為兩半分別去找兩邊的主元素，若兩邊的主元素不同則利用count方法比較出現次數，時間複雜度略優

class Solution {
public:
    int majorityElement(vector<int>
 
& nums) {
        return divideMajor(nums, 0, nums.size() - 1);
    }
    int divideMajor(vector<int>& nums, int begin, int end) {
        if (begin == end) {
            return nums[begin];
        }
        int leftM = divideMajor(nums, begin, (begin + end) / 2);
        int rightM = divideMajor(nums, (begin + end) / 2
 
 + 1, end);
        if (leftM == rightM) {
            return leftM;
        }
        if (count(nums.begin() + begin, nums.begin() + end+1, leftM) < count(nums.begin() + begin, nums.begin() + end+1, rightM)) {
            return rightM;
        }
        else {
            return leftM;
        }
    }
};