【LeetCode】Majority Element

题意：

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.

思路：

在数组中找出出现次数大于 n/2 的数。

C++ 中map 对于这种统计次数的问题来说特别方便，而 Python 的话当然用字典。

代码：

C++

class Solution{
public:
    int majorityElement(vector<int> &num) {
        vector<int>::iterator it = num.begin();
        int n = num.size();
        map<int,int> count;
        for(;it != num.end();it++)
        {
            // 这里为什么不用判断键是否存在？因为不存在时初始化为 0
            if(++count[*it] > n/2)
            {
                return *it;
            }
        }
    }
};

Python：

class Solution:
    # @param num, a list of integers
    # @return an integer
    def majorityElement(self, num):
        count = dict([])
        flag = len(num)/2
        for item in num:
            if item in count:
                count[item] = count[item] + 1
            else:
                count[item] = 1

            if count[item] > flag:
                return item