20+ Paytm Full Stack Developer Interview Questions and Answers

Program to compute factorial of a given integer 'n', with error handling for negative values.

• Create a function to calculate factorial using a loop or recursion

• Check if input is negative, return 'Error' if true

• Handle edge cases like 0 and 1 separately

• Return the calculated factorial value

The task is to find the number of distinct ways to climb from the 0th step to the Nth step, where each time you can climb either one step or two steps.

• Use dynamic programming to solve this problem

• Create an array to store the number of ways to reach each step

• Initialize the first two elements of the array as 1 and 2

• For each subsequent step, the number of ways to reach that step is the sum of the number of ways to reach the previous two steps

• Return the number of ways to reach th...read more

Determine the length of the shortest contiguous subarray that needs to be sorted to make the entire array sorted in ascending order.

• Iterate from left to right to find the first element out of order.

• Iterate from right to left to find the last element out of order.

• Calculate the length of the subarray between the two out of order elements.

Ceil value of a key in a Binary Search Tree (BST) is the smallest integer greater than or equal to the given number.

• Traverse the BST to find the closest integer greater than or equal to the given key.

• Compare the key with the current node value and update the ceil value accordingly.

• Recursively traverse left or right subtree based on the key value to find the ceil value.

• Return the ceil value once found for each test case.

Sort an integer array containing only 0s, 1s, and 2s in linear time complexity.

• Use three pointers to keep track of 0s, 1s, and 2s while traversing the array.

• Swap elements based on the values encountered to sort the array in-place.

• Time complexity should be O(N) to solve the problem efficiently.

The task is to find the Next Greater Element for each element in a list of integers.

• Iterate through the list of integers from right to left

• Use a stack to keep track of elements whose NGE is yet to be found

• Pop elements from the stack until a greater element is found or the stack is empty

• Assign the NGE as the top element of the stack or -1 if the stack is empty

Determine if two nodes in a binary tree are cousins based on level and parent nodes.

• Traverse the binary tree to find the levels and parents of the given nodes.

• Check if the nodes are at the same level and have different parents to determine if they are cousins.

• Return 'YES' if the nodes are cousins, 'NO' otherwise.

• Example: For input '1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1' and nodes 4 7, output is 'YES'.

The task is to compute the modulus of the difference between the sum of nodes at odd levels and the sum of nodes at even levels in a binary tree.

• Traverse the binary tree level by level and calculate the sum of nodes at odd and even levels separately.

• Find the absolute difference between the sums and return the modulus of this difference.

• Handle null nodes by skipping them during the sum calculation.

The task is to find the minimum number of characters needed to be added to the front of a string to make it a palindrome.

• Iterate through the string from both ends and count the number of characters that need to be added to make it a palindrome.

• Use two pointers approach to compare characters from start and end of the string.

• Keep track of the count of characters needed to be added to form a palindrome.

Rotate a square matrix by 90 degrees in an anti-clockwise direction using constant extra space.

• Iterate through each layer of the matrix from outer to inner layers

• Swap elements in groups of 4 to rotate the matrix

• Handle odd-sized matrices by adjusting the center element if needed

Find the Lowest Common Ancestor (LCA) of two nodes in a Binary Search Tree (BST).

• Traverse the BST from the root node to find the LCA of the given nodes.

• Compare the values of the nodes with the values of P and Q to determine the LCA.

• If the values of P and Q are on opposite sides of the current node, then the current node is the LCA.

The task is to find the maximum amount of money Mr. X can rob from houses arranged in a circle without alerting the police.

• The problem can be solved using dynamic programming.

• Create two arrays to store the maximum amount of money robbed when considering the first house and when not considering the first house.

• Iterate through the array and update the maximum amount of money robbed at each house.

• The final answer will be the maximum of the last element in both arrays.

Find the minimum time required to rot all fresh oranges in a grid.

• Create a queue to store the rotten oranges and their time of rotting.

• Iterate through the grid to find all rotten oranges and add them to the queue.

• Simulate the rotting process by checking adjacent cells and updating their status.

• Track the time taken to rot all fresh oranges and return the result.

• Handle edge cases like unreachable fresh oranges or already rotten oranges.

Determine if one binary tree is a subtree of another binary tree based on their structure and node values.

• Traverse through the main tree and check if any subtree matches the second tree

• Use recursion to compare nodes of both trees

• Handle edge cases like empty trees or null nodes

• Check if the root node of the second tree exists in the main tree

Find the Kth smallest and largest elements in an array.

• Sort the array to easily find the Kth smallest and largest elements.

• Ensure K is within the array's size to avoid errors.

• Handle multiple test cases efficiently.

• Consider edge cases like when N is small or K is at the extremes.

Given a sorted N * N matrix, find the position of a target integer 'X'.

• Iterate over rows and columns to search for the target integer 'X'.

• Utilize the sorted nature of the matrix to optimize the search process.

• Return the position of 'X' if found, else return '-1 -1'.

Move all even numbers to the beginning and odd numbers to the end of an array.

• Iterate through the array and swap even numbers to the front and odd numbers to the back.

• Use two pointers, one starting from the beginning and one from the end, to achieve the desired arrangement.

• Return the modified array with even numbers at the start and odd numbers at the end.

Determine if two strings are anagrams of each other by checking if they have the same characters in different order.

• Create a character frequency map for both strings and compare them.

• Sort both strings and compare if they are equal.

• Use a hash table to store character counts and check if they are the same for both strings.

Find the longest palindromic substring in a given string, returning the rightmost one if multiple exist.

• Iterate through each character in the string and expand around it to find palindromes

• Keep track of the longest palindrome found and its starting index

• Return the substring starting from the index of the longest palindrome found

Determine if it is possible to complete all tasks considering prerequisites.

• Create a graph representation of the tasks and dependencies.

• Use topological sorting to check if there is a cycle in the graph.

• Return 'Yes' if no cycle is found, 'No' otherwise.

Calculate the total amount of rainwater that can be trapped between given elevations in an array.

• Iterate through the array and calculate the maximum height on the left and right of each bar.

• Calculate the amount of water that can be trapped at each bar by taking the minimum of the maximum heights on the left and right.

• Sum up the trapped water at each bar to get the total trapped water for the entire array.

Determine if a robot's movement path is circular on a 2D grid given a sequence of moves.

• Iterate through the move sequence and update the robot's position based on the moves ('L' - turn left, 'R' - turn right, 'G' - move forward).

• Check if the robot returns to the starting position after completing the move sequence.

• If the robot ends up at the starting position and facing the north direction, the movement path is circular.

Find all the bridges in an undirected graph by identifying edges that, when removed, increase the number of connected components.

• Use Tarjan's algorithm to find bridges in the graph.

• Keep track of the discovery time and low time of each vertex during DFS traversal.

• An edge (u, v) is a bridge if low[v] > disc[u].

• Handle multiple test cases efficiently to find bridges in each graph.

• Ensure the output contains the count of bridges and the vertices defining each bridge.

A Linked List in Java is implemented using nodes with references to the next node. It is preferred over an ArrayList when frequent insertions and deletions are required.

• In Java, a Linked List is implemented using a Node class with data and a reference to the next Node.

• LinkedList class in Java provides methods like add(), remove(), and get() for manipulating the list.

• Linked List is preferred over ArrayList when frequent insertions and deletions are needed due to its constant-t...read more

Paytm is a leading Indian digital payment platform offering a wide range of services including mobile recharges, bill payments, and online shopping.

• Founded in 2010 by Vijay Shekhar Sharma

• Offers services like mobile recharges, bill payments, online shopping, and digital wallet

• Acquired by One97 Communications in 2013

• Expanded into financial services like Paytm Payments Bank and Paytm Money

• One of the largest digital payment platforms in India