334. Increasing Triplet Subsequence (Medium)

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.

class Solution {
public:
    bool increasingTriplet(vector<int>& nums) {
        int min1 = INT_MAX, min2 = INT_MAX;
        for (int n: nums) {
            if (n > min2) return true;
            if (n <= min1) min1 = n;
            else if (n < min2) min2 = n;
        }
        return false;
    }
};