414. Third Maximum Number

Given an integer array nums, return the third distinct maximum number in this array. If the third maximum does not exist, return the maximum number.

Example 1:

Input: nums = [3,2,1]
Output: 1
Explanation:
The first distinct maximum is 3.
The second distinct maximum is 2.
The third distinct maximum is 1.

Example 2:

Input: nums = [1,2]
Output: 2
Explanation:
The first distinct maximum is 2.
The second distinct maximum is 1.
The third distinct maximum does not exist, so the maximum (2) is returned instead.

Example 3:

Input: nums = [2,2,3,1]
Output: 1
Explanation:
The first distinct maximum is 3.
The second distinct maximum is 2 (both 2's are counted together since they have the same value).
The third distinct maximum is 1.

Constraints:

• 1 <= nums.length <= 104
• -231 <= nums[i] <= 231 - 1

Follow up: Can you find an O(n) solution?

Solution:

class Solution {
    public int thirdMax(int[] nums) {
        Integer first = null; 
        Integer second = null;
        Integer third = null;

        for (int num : nums){
            if (Objects.equals(num, first) || Objects.equals(num, second) || Objects.equals(num, third)){
                continue;
            }

            if (first == null || num > first){
                third = second;
                second = first;
                first = num;
            }else if (second == null || num > second){
                third = second;
                second = num;
            }else if (third == null || num > third){
                third = num;
            }
        }
        if (third != null){
            return third;
        }else {
            return first;
        }
    }
}

// TC: O(n)
// SC: O(1)

这题题意理解怪怪的.

要求在一个整数数组 nums 中找到第 3 大的不同数字，如果不存在第 3 大的数，就返回最大数.