Paytm Interview – Software Engineer

Hello guys, I am having a 1.3 year of experience and I applied in Paytm money for software engineer profile.

Round 1: online test.

Round 2: all algorithm questions.

Round 3: algorithm + java + spring boot framework.

Round 4: projects + 1 algorithm + query optimization.

Online test(1 hrs):-

   1. Coin change problem modified version, time O(n*n).

   2. Balanced parenthesis problem, and print longest braces length, time O(n).


  1. Give tree is bst.   O(n) time complexity, space O(1)
  2. Maximum sub array without breaking.   O(n) time complexity, space O(1)
  3. Lca of a binary tree.  O(n) time complexity, space O(1)
    GeeksforGeeks Link
  4. The distance between 2 nodes in tree. O(n) time complexity, space O(1)
    GeeksforGeeks Link
  5. Find minkey in stack O(1) time complexity, space O(1)*.
  6. array contains 0, 1, 2 sort in O(n) time and O(1) space, in-place sorting.
    GeeksforGeeks Link
  7. Find second highest element In array of integer with code optimization.
    GeeksforGeeks Link


   1. Internal implementation of HashMap.

   2. Difference b/w Abstract and interface. GeeksforGeeks Link

   3. write a custom class to achieve Mutability.

   4. Java multithreading with both approach differences.

Spring boot:-

   1. Dependencies of injection, inversion of control.

   2. Some annotations.

   3. What’s the problem we are facing without Dependencies of injection.


   1. Ask current working project with some internal and deeper discussion.

   2. Query optimization and some internal working of the database which I was using in my current project.

Optimize the query:-

Select a, b, c from table where d=* and e=*;


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