[LeetCode] 414. Third Maximum Number

轉自LeetCode

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.

<Solution>

C++ 可以使用 set 這個資料結構，會主動排序

因此，只要 set 的大小大於三，就把最小的砍掉

code 如下

C++

	class Solution {
	public:
	int thirdMax(vector<int>& nums) {
	set<int> top3;
	for(const auto &n : nums) {
	top3.insert(n);
	if(top3.size() > 3) {
	top3.erase(top3.begin());
	}
	}
	return top3.size() == 3 ? *top3.begin() : *top3.rbegin();
	}
	};

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