Paytm Interview Experience ( Backend Developer )

Round 1: First Round was coding round. Two questions were there. (1 hr)

  1. In given integer array, if any integer is repeating then replace it with a number greater than that number which has not been inserted yet in the array. Eg. 1, 3, 4, 5, 3       Output: 1, 3, 4, 5, 6
  2. Find a longest common subsequence that all the characters present in the subsequence should be of vowels
    Eg : String 1: aieef     String 2: klaied     Answer: 3 (aie)

Round 2: Second Round was technical round ( 1hr – 1:15hr)

  1. What is multithreading?
  2. Sort an array containing 0 and 1 in O(n) time.
  3. Write a program to find the height of a tree.
  4. Write a program to reverse the linked list.
  5. Find an element in array in O(n) comparisons.

Round 3: Third Round was technical round ( 1hr – 1:15hr)



  1. What are semaphore and mutex?
  2. What is the internal implementation of HashMap?
  3. Write a program to find the nth Fibonacci number considering all test cases.
  4. Write a program to check if the binary tree is height balanced or not.

Round 4: This was Manager Round of Discussion ( 1 hr )

  1.  What is HashMap?
  2. What should be done if we need the HashMap key to be of any User Defined Type? Eg. An object of any class?
  3. Implement a class whose object is immutable, like String Class.
  4. Discussion of my projects.


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