> For the complete documentation index, see [llms.txt](https://dfine.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dfine.gitbook.io/leetcode/414.third_maximum_number.md).

# 414.Third Maximum Number

**414.Third Maximum Number**

难度:Easy

> 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.
```

topK用最小堆，去重用set。

```
class Solution {
public:
    int thirdMax(vector<int>& nums) {
        if(nums.size()<3) return *max_element(nums.begin(),nums.end());
        priority_queue<int,vector<int>,greater<int>>three;
        unordered_set<int>ele;

        for(int i=0;i<nums.size();i++)
        {
            if(ele.count(nums[i])) continue;
            three.push(nums[i]);
            ele.insert(nums[i]);
        }
        if(three.size()==1) return three.top();
        if(three.size()==2)    {three.pop();    return three.top();}
        while(three.size() !=3) three.pop();
        return three.top();
        
    }
};
```

> 执行用时 :24 ms, 在所有 C++ 提交中击败了13.20%的用户\
> 内存消耗 :10.8 MB, 在所有 C++ 提交中击败了5.05%的用户


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