Increasing Triplet Subsequence

Increasing Triplet Subsequence array

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, ksuch 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.

Increasing Triplet Subsequence Solution

public class IncreasingTripletSequence {
    public boolean increasingTriplet(int[] nums) {
        int firstMin = Integer.MAX_VALUE;
        int secondMin = Integer.MAX_VALUE;

        for(int n : nums) {
            if(n <= firstMin) {
                firstMin = n;
            } else if(n < secondMin) {
                secondMin = n;
            } else if(n > secondMin) {
                return true;
            }
        }

        return false;
    }
}

Last modified October 4, 2020