Increasing Triplet Subsequence in Python

Suppose there is an unsorted array. We have to check whether an increasing subsequence of length 3 exists or not in that 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.

To solve this, we will follow these steps −

• small := infinity, big := infinity
• for each element i in array
  • if i <= small, then small := i, otherwise when i <= big, then big := i, otherwise return true
• return false

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Solution(object):
   def increasingTriplet(self, nums):
      small,big = 100000000000000000000,100000000000000000000
      for i in nums:
         if i <= small:
            small = i
         elif i<=big:
            big = i
         else :
            return True
      return False
ob1 = Solution()
print(ob1.increasingTriplet([5,3,8,2,7,9,4]))

Input

[5,3,8,2,7,9,4]

Output

True