PhonePe Site Reliability Engineer Interview Questions, Process, and Tips

Round duration - 60 minutes
Round difficulty - Medium

It was held in the evening around 4 pm. The camera was on during the test to invigilate the activity of students. On any doubtful action, warning was given. Platform was easy to code in.

Q1. 
Replace 0s Problem Statement
You are given a matrix where every element is either a 1 or a 0. The task is to replace 0 with 1 if it is surrounded by 1s. A 0 (or a set of 0s) is considered to be surrounded...read more
Ans. 
Given a matrix of 1s and 0s, replace 0s surrounded by 1s with 1s.
• Iterate through the matrix and check each 0 surrounded by 1s.

• If a 0 is surrounded by 1s, replace it with 1.

• Update the matrix in place without printing or returning it.
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Q2. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
The task is to determine the total number of ways to make change for a specified value using given denominations.
• Use dynamic programming to keep track of the number of ways to make change for each value up to the target value.

• Iterate through each denomination and update the number of ways to make change for each value based on the current denomination.

• Handle base cases such as making change for 0 or using only the smal...read more
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Q3. 
Minimum Subset Sum Difference Problem
Given an array of non-negative integers, your task is to partition this array into two subsets such that the absolute difference between the sums of the subsets is mi...read more
Ans. 
Given an array, partition it into two subsets to minimize the absolute difference between their sums.
• Use dynamic programming to calculate all possible subset sums.

• Iterate through the subset sums to find the minimum absolute difference.

• Consider all possible partitions of the array elements.

• Example: For input [1, 6, 11, 5], the minimum absolute difference is 1.

• Example: For input [1, 2, 3], the minimum absolute difference
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Round duration - 60 minutes
Round difficulty - Medium

It was held in the morning around 11:30 am. The interview was scheduled on google meet. The interviewer was quite friendly. He started by a brief introduction. This round was mostly based on Data structures and algorithms. At the end he asked some concepts of OOPs and Operating System.

Q1. 
String Transformation Problem
Given a string (STR) of length N, you are tasked to create a new string through the following method:
Select the smallest character from the first K characters of STR, remov...read more
Ans. 
Given a string and an integer K, create a new string by selecting the smallest character from the first K characters of the input string and repeating the process until the input string is empty.
• Iterate through the input string, selecting the smallest character from the first K characters each time.

• Remove the selected character from the input string and append it to the new string.

• Continue this process until the input ...read more
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Q2. 
SpecialStack Design Problem
Design a stack that efficiently supports the getMin() operation in O(1) time with O(1) extra space. This stack should include the following operations: push(), pop(), top(), is...read more
Ans. 
Design a stack that supports getMin() operation in O(1) time with O(1) extra space using inbuilt stack data structure.
• Use two stacks - one to store the actual data and another to store the minimum value at each level.

• When pushing a new element, check if it is smaller than the current minimum and update the minimum stack accordingly.

• When popping an element, also pop the top element from the minimum stack if it matches t...read more
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Q3. 
Geometric Progression Subsequences Problem Statement
Given an array of ‘N’ integers, determine the number of subsequences of length 3 that form a geometric progression with a specified common ratio ‘R’.
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Ans. 
Count the number of subsequences of length 3 forming a geometric progression with a specified common ratio in an array of integers.
• Iterate through the array and for each element, check for possible subsequences of length 3 with the given common ratio.

• Use a hashmap to store the count of possible subsequences for each element as the middle element.

• Return the total count of subsequences modulo 10^9 + 7.

• Example: For input ...read more
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Q4. What are the conditions for a deadlock to occur?
Ans. 
Deadlock occurs when two or more processes are waiting for each other to release resources, resulting in a standstill.
• Two or more processes must be holding resources and waiting for resources held by other processes

• Processes cannot proceed because they are stuck in a circular wait

• Resources cannot be forcibly released by the operating system

• Examples: Process A holds Resource 1 and waits for Resource 2, while Process B h
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Round duration - 45 minutes
Round difficulty - Medium

It was held in the afternoon around 3pm. The interviewer was quite friendly. She started with my introduction. She asked 2-3 problems related to data structures and then asked about python libraries which I used in my projects.

Q1. 
Group Anagrams Problem Statement
Given an array or list of strings called inputStr, your task is to return the strings grouped as anagrams. Each group should contain strings that are anagrams of one anoth...read more
Ans. 
Group anagrams in an array of strings based on their characters.
• Iterate through each string in the input array/list.

• For each string, sort the characters alphabetically to create a key for grouping.

• Use a hashmap to group strings with the same key.

• Return the grouped anagrams as separate arrays of strings.
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Q2. 
Kth Smallest Element Problem Statement
You are provided with an array of integers ARR of size N and an integer K. Your task is to find and return the K-th smallest value present in the array. All elements...read more
Ans. 
Find the K-th smallest element in a given array of distinct integers.
• Sort the array in ascending order.

• Return the element at index K-1 from the sorted array.

• Handle edge cases like K being out of bounds or array being empty.
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Round duration - 45 minutes
Round difficulty - Medium

It was held in the evening around 6 pm. The interviewer started with a brief introduction of me. He asked about my projects and then asked some concepts of Operating System and problems related to data structures. I had projects of Machine Learning and Deep learning. Discussion about projects continued for about 25 minutes.

Q1. 
Middle of a Linked List
You are given the head node of a singly linked list. Your task is to return a pointer pointing to the middle of the linked list.
If there is an odd number of elements, return the ...read more
Ans. 
Return the middle element of a singly linked list, or the one farther from the head node if there are even elements.
• Traverse the linked list with two pointers, one moving twice as fast as the other

• When the fast pointer reaches the end, the slow pointer will be at the middle

• Return the element pointed to by the slow pointer
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