LeetCode 414. Third Maximum Number

原题链接在这里：https://leetcode.com/problems/third-maximum-number/

题目：

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.

题解：

设立三个指针，交替赋值.

Time Complexity: O(n), n = nums.length.

Space: O(1).

AC Java:

public class Solution {
    public int thirdMax(int[] nums) {
        Integer max1 = null;
        Integer max2 = null;
        Integer max3 = null;
        
        for(Integer n : nums){
            if(n.equals(max1) || n.equals(max2) || n.equals(max3)){
                continue;
            }
            
            if(max1==null || n>max1){
                max3 = max2;
                max2 = max1;
                max1 = n;
            }else if(max2==null || n>max2){
                max3 = max2;
                max2 = n;
            }else if(max3==null || n>max3){
                max3 = n;
            }
        }
        
        return max3 == null ? max1 : max3;
    }
}

类似Kth Largest Element in an Array.