leet code - Third Maximum Number

题目描述
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).


返回数组中第三大的数字，可能会包含重复。


思路：
直接遍历过程中存最大值求出结果。

public class Solution {    public int ThirdMax(int[] nums)     {if(nums == null || nums.Length == 0){throw new ArgumentException();}if(nums.Length == 1){return nums[0];}if(nums.Length == 2){return Math.Max(nums[0],nums[1]);}int max = nums[0];for(var i = 1;i < nums.Length; i++){if(nums[i] > max){max = nums[i];}}int? second = null;for(var i = 0;i < nums.Length; i++){if(nums[i] < max && (second == null || nums[i] > second)){second = nums[i];}}if(!second.HasValue){return max;}int? third = null;for(var i = 0;i < nums.Length; i++){if(nums[i] < second && (third == null || nums[i] > third)){third = nums[i];}}if(third.HasValue){return third.Value;}else{return max;}}}