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.

class Solution {
public:
    bool increasingTriplet(vector& nums) {
        int n = nums.size();
        int a = INT_MAX;
        int b = INT_MAX;

        for (int i = 0; i < n; i++)
        {
            if (nums[i] <= a)
            {
                a = nums[i];
            }
            else if (nums[i] <= b)
            {
                b = nums[i];
            }
            else
            {
                return true;
            }
        }

        return false;
    }
};