Leetcode 334: Increasing Triplet Subsequence

Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.

Formally the function should:

Return true if there exists i, j, k 
such that arr[i] < arr[j] < arr[k] given 0 ≤ i < j < k ≤ n-1 else return false.

 

Your algorithm should run in O(n) time complexity and O(1) space complexity.

Examples:
Given [1, 2, 3, 4, 5],
return true.

Given [5, 4, 3, 2, 1],
return false.

 

public class Solution {
    public bool IncreasingTriplet(int[] nums) {
        if (nums == null || nums.Length < 3) return false;
        int min = Int32.MaxValue, secondMin = Int32.MaxValue;
        
        for (int i = 0; i < nums.Length; i++)
        {
            if (nums[i] <= min)
            {
                min = nums[i];
            }
            else if (nums[i] <= secondMin)
            {
                secondMin = nums[i];
            }
            else
            {
                return true;
            }
        }
        
        return false;
    }
}