Increasing Triplet Subsequence

Desicription

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.
Note: Your algorithm should run in O(n) time complexity and O(1) space complexity.

Example 1:

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Input: [1,2,3,4,5]
Output: true

Example 2:

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Input: [5,4,3,2,1]
Output: false

Solution

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class Solution {
public:
bool increasingTriplet(std::vector<int>& nums) {
int c1 = INT_MAX;
int c2 = INT_MAX;
for(auto num : nums) {
if(num <= c1) {
c1 = num;
} else if(num <= c2) {
c2 = num;
} else {
return true;
}
}

return false;
}
};