334. Increasing Triplet Subsequence

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.

Credits:Special thanks to @DjangoUnchained for adding this problem and creating all test cases.

Solution

public class Solution {
   public boolean increasingTriplet(int[] nums) {
        int x = Integer.MAX_VALUE;
        int y = Integer.MAX_VALUE;

        for(int i = 0; i < nums.length; i ++) {
            int z = nums[i];

            if (x >= z) {
                x = z;
            } else if (y>=z) {
                y = z;
            } else {
                return true;
            }
        }

        return false;
    }
}