334_Increasing_Triplet_Subsequence.cpp

/*
334. Increasing Triplet Subsequence
Given an integer array nums, return true if there exists a triple of indices (i, j, k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists, return false.

 

Example 1:

Input: nums = [1,2,3,4,5]
Output: true
Explanation: Any triplet where i < j < k is valid.
Example 2:

Input: nums = [5,4,3,2,1]
Output: false
Explanation: No triplet exists.
Example 3:

Input: nums = [2,1,5,0,4,6]
Output: true
Explanation: The triplet (3, 4, 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6.
 

Constraints:

1 <= nums.length <= 5 * 105
-231 <= nums[i] <= 231 - 1
*/
class Solution {
public:
 // time Complexity O(n)
 // Space Complexity O(1)

    bool increasingTriplet(vector<int>& nums) {
        if (nums.size() < 3) {
            return false;
        }
        int a = INT_MAX;
        int b = INT_MAX;

        for (int num : nums) {
            if (num <= a) {
                a = num;
            } else if (num <= b) {
                b = num;
            } else {
                return true;
            }
        }

        return false;
    }
};