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 IncreasingTripletSubsequence {
	public static boolean increasingTriplet(int[] nums) {
        if(nums.length <= 0) return false;
        int left = Integer.MAX_VALUE, right = Integer.MAX_VALUE;
        for(int i = 0; i < nums.length; i++){
            if(nums[i] <= left){
                left = nums[i];
            }else if(nums[i] <= right){
                right = nums[i];
            }else{
                return true;
            }
        }
        return false;
    }

	public static void main(String[] args) {
           boolean p = increasingTriplet(new int[] {1, 3, 5, 7, 9, 12});
           System.out.println("Result: " + p);
	}	

}