LeetCode Array Easy 414. Third Maximum Number

 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.

 问题描述，给定要给非空数组，找出第三大的数，如果找不到则返回最大值。

思路：用三个数分别存最大 第二 第三大的值。但是由于数组中会出现int的最小边界值。所以干脆用long类型来存储前三个值。

public int ThirdMax(int[] nums) {
        long max = long.MinValue;
        long sec = long.MinValue;
        long third = long.MinValue;
        
        for(int i = 0; i < nums.Length; i++){
            int temp = nums[i];
            if(temp > max){
               third = sec;
                sec = max;
                max=temp;
            }
            else if(temp < max && temp >sec){
                third = sec;
                sec=temp;
            }
            else if(temp < sec && temp >=third){
                third = temp;
            }
                
        }
        return third > long.MinValue ? (int)third : (int)max;
    }