OLA Interview Experience (Off-Campus)

I applied to OLA in off campus drive for Full Stack Developer role. 

Round 1. First round was telephonic round. First question was tell me about yourself then I was asked few questions from OOP in rapid fire manner then basic approach as to how to reverse alternate nodes in a linked list without modifying the data of the linked list, next question was how many tree traversals are required and which all to identify a unique tree, last question was three ants and a triangle puzzle, then the Interviewer asked me to derive a generalized formula for the same puzzle for n-sided shape. Interview lasted for approximately 45 minutes, I hustled a bit on 2nd question but after a hint was able to solve it. 

1. Given a linked list, reverse alternate nodes 

2. If you are given two traversal sequences, can you construct the binary tree?

3. Ants and triangle puzzle.

Round 2. Second round was Online Test on Hackerrank for 120 minutes, it contained 5 questions mainly on arrays, strings and LRU cache. 

Round 3. Third round was face to face Interview at Ola Campus, Interviewer started with discussing projects done in Internship at Honeywell and IIT BHU after that he gave a simple question to reverse words in a given string and write code for it, second question was to find first occurrence of 0 in a sorted array of 0s and 1s, I gave a binary search approach and he was satisfied by it, next he complicated the question by making the size of the array infinite, after a hint I was able to come up with binary search approach in which the end index would double up each time the binary search was called, he looked convinced and this round lasted for about an hour. 

1. Reverse words in a given string

2. First index of 1 in a sorted array

3. First index of 1 in an infinite sorted array.

Round 4. Fourth round was again a face to face technical Interview, I was just asked one question in this round, given an array of strings print the k most frequent occurring strings, I gave an approach using k sized max heap, after getting satisfied with the approach the Interviewer asked me to code it, I missed a boundary case of the array of strings being empty which the Interviewer pointed out and asked me to cover it along with other such cases, I modified the code for such conditions and upon 2nd review the Interviewer was satisfied. This round also lasted for about an hour. 

1. K most frequent words. 

Round 5. Fifth round was managerial round, in this they gave me a question to design a toll booth system for the Ola cabs and explain the necessary functions and data structures used in it, the manger also had a short discussion on my Internship at GeeksforGeeks and asked me to explain few articles written during the Internship, I extensively talked about the cab allocation article written during my Internship at GeeksforGeeks. This round lasted for about 40 minutes. 

1. Finding cabs nearby.

Round 6. Sixth round was HR round, they asked me general questions like what are your strengths and weaknesses, why do you want to join Ola, salary expectations, etc. The HR round was short and barely lasted for 30 minutes. 

After the HR round I was amongst the 6-7 people selected in the off-campus hiring conducted by them.