334. Increasing Triplet Subsequence

Problem:

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.

Solutions:

public class Solution {
    public boolean increasingTriplet(int[] nums) {
        int min = Integer.MAX_VALUE;
        int mid = Integer.MAX_VALUE;
        for (int i = 0; i < nums.length; i ++) {
            if (nums[i] > mid) {
                return true;
            }
            if (nums[i] < min) {
                min = nums[i];
            }
            else if (nums[i] > min) {
                mid = nums[i];
            }
        }
        return false;
    }
}