IncreasingTripletSubsequence.java

// 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 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;
    }
}