leetcode 414. Third Maximum Number 第三大数据

Given a non-empty array of integers, return the third maximum number in this array. If it does not exist, return the maximum number. The time complexity must be in O(n).

Example 1:
Input: [3, 2, 1]

Output: 1

Explanation: The third maximum is 1.
Example 2:
Input: [1, 2]

Output: 2

Explanation: The third maximum does not exist, so the maximum (2) is returned instead.
Example 3:
Input: [2, 2, 3, 1]

Output: 1

Explanation: Note that the third maximum here means the third maximum distinct number.
Both numbers with value 2 are both considered as second maximum.

本提题意就是寻找第三大的数据，这里我们使用一个set来表示，注意set是一个高度平衡的二叉搜索树，所以注意set数据结构的使用

set–常见成员函数及基本用法

代码如下：

#include <iostream>#include <vector>#include <map>#include <set>#include <queue>#include <stack>#include <string>#include <climits>#include <algorithm>#include <sstream>#include <bitset>using namespace std;class Solution{public:    int thirdMax(vector<int>& nums)    {        set<int> ss;        for (int i : nums)        {            ss.insert(i);            if (ss.size() > 3)                ss.erase(ss.begin());        }        if(ss.size()==3)            return *(ss.begin());        else            return *(ss.rbegin());    }};