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.

Solution similar to longest increasing subsequence

class Solution {
public:
    bool increasingTriplet(vector<int>& nums) {
        int n = nums.size();
        if ( n <= 2 ) return false;
        int m1 = nums[0], m2 = INT_MAX;
        for ( int i = 1; i <= n-1; i++ ) {
            int ni = nums[i];
            if ( ni > m2 ) return true;
            if ( ni <= m1 ) m1 = ni;
            else m2 = ni;
        }
        return false;
    }
};