334. Increasing Triplet Subsequence

/**
 * Refer:
 * https://leetcode.com/problems/increasing-triplet-subsequence/discuss/79004/Concise-Java-solution-with-comments.
 *
 * Time Complexity: O(N)
 *
 * Space Complexity: O(1)
 *
 * N = Length of the input array.
 */
class Solution {
    public boolean increasingTriplet(int[] nums) {
        if (nums == null || nums.length < 3) {
            return false;
        }

        int c1 = Integer.MAX_VALUE;
        int c2 = Integer.MAX_VALUE;

        for (int num : nums) {
            if (num <= c1) {
                // update c1 if num is smaller than both c1 & c2.
                c1 = num;
            } else if (num <= c2) {
                // update c2 only if num is greater than c1 but smaller than c2.
                c2 = num;
            } else {
                // return true if found a number bigger than both c1 & c2.
                return true;
            }
        }

        return false;
    }
}