LeetCode: Increasing Triplet Subsequence

Find if there exists an increasing triplet subsequence in an array.

Solution

The constraints state that the maximum value is 2^31 - 1. This is used as the initial values for first and second.

Loop through each val in nums.

• If val is equal to first or second, do nothing.
• If val is less than first, update first to be val.
• If val is less than second, update second to be val. This means that second is guaranteed to be strictly greater than first.
• Otherwise, return True. This guarantees that val is greater than both first and second.

class Solution:
    def increasingTriplet(self, nums: List[int]) -> bool:
        first = 2 ** 31 - 1
        second = 2 ** 31 - 1

        for val in nums:
            if val == first or val == second:
                pass
            elif val < first:
                first = val
            elif val < second:
                second = val
            else:
                return True

        return False