Array Math

Description:

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.

刚开始不会写，想先排序再找，发现超级麻烦，就放弃了，看了Discuss，直接用数学的方法来比较大小就好，我感觉我永远都get不到题目想让我怎么解....

public class Solution {

    public int thirdMax(int[] nums) {

        Integer num1 = null;

        Integer num2 = null;

        Integer num3 = null;

        for (Integer num : nums) {

            if (num.equals(num1) || num.equals(num2) || num.equals(num3)) continue;

            if (num1 == null || num > num1) {

                num3 = num2;

                num2 = num1;

                num1 = num;

            } else if (num2 == null || num > num2) {

                num3 = num2;

                num2 = num;

            } else if (num3 == null || num > num3) {

                num3 = num;

            }

        }

        return num3 == null ? num1 : num3;

    }

}