400+ Interview Questions and Answers

Ninja loves playing with numbers. So one day, he wants to arrange a few numbers in the ‘N’ number of rows. The first row contains 1 number, the second row has two numbers, the third row has 3 digit...read more

Ninja has been given a program to do basic string compression. For a character that is consecutively repeated more than once, he needs to replace the consecutive duplicate occurrences with th...read more

Ninja has organized the new year party and invited all the programmers for it, as being the programmer also has been invited by Ninja.

To detect whether the guest is a programmer or...read more

Given an array ‘ARR’ of size ‘N,’ swap the Kth element from beginning with the Kth element from the end.

For example:

If ‘N’ = 5 and K = 2 [1, 2, 3, 4, 5] Then the output will be [1, 4, 3, 2, 5...read more

You are given an array (ARR) of length N, consisting of integers. You have to find the sum of the subarray (including empty subarray) having maximum sum among all subarrays.

A subarray is a ...read more

You are given the schedule of N meetings with their start time Start[i] and end time End[i]. But you have only 1 meeting room. So, you need to tell the meeting numbers you can organize in the gi...read more

Given a number N, figure out if it is a member of fibonacci series or not. Return true if the number is member of fibonacci series else false.

Fibonacci Series is defined by the recurrence

 F(n)...read more

You are given an infinite supply of coins of each of denominations D = {D0, D1, D2, D3, ...... Dn-1}. You need to figure out the total number of ways W, in which you can make a change fo...read more

For a given array with N elements, you need to find the length of the longest subsequence from the array such that all the elements of the subsequence are sorted in strictly increa...read more

Two players 'X' and 'Y', are playing a coin game. Initially, there are 'N' coins. Each player can pick exactly 'A' coins or 'B' coins or 1 coin. A player los...read more

You have been given a permutation of ‘N’ integers. A sequence of ‘N’ integers is called a permutation if it contains all integers from 1 to ‘N’ exactly once. Your task is to rearrange the number...read more

You have been given an array/list ARR consisting of ‘N’ elements. Each element in the array is either 0, 1 or 2.

Now, your task is to sort this array/list in increasing order. For ...read more

You are given with an array of integers and an integer K. You have to find and print the count of all such pairs which have difference K.

Note: Take absolute difference between the elemen...read more

You are given an array/list 'ARR' consisting of N integers, which contains elements only in the range 0 to N - 1. Some of the elements may be repeated in 'ARR'. Your task is to find all ...read more

You have been given a number of stairs. Initially, you are at the 0th stair, and you need to reach the Nth stair. Each time you can either climb one step or two steps. You are...read more

You have been given a long type array/list 'ARR' of size 'N'. It represents an elevation map wherein 'ARR[i]' denotes the elevation of the 'ith' bar. Print the total amount of rainwater that ...read more

A few days back, Ninja encountered a string containing characters from ‘A’ to ‘Z’ which indicated a secret message. For security purposes he encoded each character of the string to its numeric v...read more

You are given a positive integer ‘N’. You are required to print the perfect square number closest to the ‘N’ and the number of steps required to reach that number.

For Example:

N = 21 The ...read more

Given a string ’S’ consisting of lower case English letters, you are supposed to return the longest palindromic substring of ‘S’.

Note that in case of more than one longest palindro...read more

You are given a number 'N'. Your task is to find Nth prime number.

A prime number is a number greater than 1 that is not a product of two smaller natural numbers. Prime numbers have only two facto...read more

Given an array ‘ARR’ of ‘N’ integers, where all the elements occur an even number of times and only one number occurs an odd number of times. Find the number which occurs an odd number of times.

E...read more

Given a positive integer ‘n’, your task is to find the next smallest integer and the previous largest integer having the exact number of ‘1’ bits set in their bin...read more

Ninja developed a love for arrays and strings so this time his teacher gave him an array of strings, ‘A’ of size ‘N’. Each element of this array is a string. The teacher taught Ninja about prefix...read more

You are given a string 'S'. Your task is to check whether the string is palindrome or not. For checking palindrome, consider alphabets and numbers only and ignore the symbols ...read more

You are given an array Arr consisting of N integers. You need to find the equilibrium index of the array.

An index is considered as an equilibrium index if the sum of elements of the array to t...read more

You're given string ‘STR’ consisting solely of “{“, “}”, “(“, “)”, “[“ and “]” . Determine whether the parentheses are balanced.

Input Format:

The first line contains an Integer 'T' which denot...read more

A few days back, Ninja encountered a string containing characters from ‘A’ to ‘Z’ which indicated a secret message. For security purposes he encoded each character of the stri...read more

A thief is robbing a store and can carry a maximum weight of ‘W’ into his knapsack. There are 'N' items available in the store and the weight and value of each item is known to the thief. Consideri...read more

You are given a binary tree in which each node contains an integer value and a number ‘K’. Your task is to print every path of the binary tree with the sum of nodes in the path as ‘...read more

You are given a sentence in the form of a string ‘S’. You have to convert ‘S’ into its equivalent mobile numeric keypad sequence, i.e. print the sequence in such a way that if it is typed on the...read more

You are given a positive integer ‘N’. Your task is to print all prime numbers less than or equal to N.

Note: A prime number is a natural number that is divisible only by 1 and itself. Example ...read more

How do we measure forty-five minutes using two identical wires, each of which takes an hour to burn? We have matchsticks with us. The wires burn non-uniformly. So, for example, the two halves of ...read more

You are given an array of integers "ARR" of length 'N' and an integer 'K'. Your task is to find whether or not you can divide the array "ARR" into 'K' subsets with equal sum.

A subset of...read more

You are given a string 'STR' containing lowercase English letters from a to z inclusive. Your task is to find all non-empty possible subsequences of 'STR'.

A Subsequence of a string is the...read more

A Derangement is a permutation of ‘N’ elements, such that no element appears in its original position. For example, an instance of derangement of {0, 1, 2, 3} is {2, 3, 1, 0}, because 2 presen...read more

You are given an array 'ARR' consisting of 'N' integers. You need to rearrange the array elements such that all negative numbers appear before all posit...read more

A thief is robbing a store and can carry a maximal weight of W into his knapsack. There are N items and the ith item weighs wi and is of value vi. Considering the constraints of the maximum weight t...read more

Given two 1-dimensional arrays containing strings of lowercase alphabets, print the elements that are common in both the arrays i.e. the strings that are present in both the arrays.

Note:

An elem...read more

Write a program to count and print the total number of characters (lowercase english alphabets only), digits (0 to 9) and white spaces (single space, tab i.e. '\t' and newline i.e. '\n') entered...read more

You are given the first term (A), the common ratio (R) and an integer N. Your task is to find the Nth term of the GP series.

The general form of a GP(Geometric Progression) series is A, A(R), A(R...read more

You are given an array ‘arr’ of size ‘N’ and an integer ‘K’. Your task is to find the maximum subset-sum of the array that is not greater than ‘K’.

For Example:

Your are given ‘arr’ = [1, 3, 5, 9],...read more

You are given an integer N, you need to find the number of trailing zeroes in N! (N factorial).

Note:

1. Trailing zeros in a number can be defined as the number of continuous suffix z...read more

Given a string S containing digits from 2 to 9 inclusive. Your task is to find all possible letter combinations that the number could represent.

A mapping from Digits to Le...read more

You are given the arrival and departure times of N trains at a railway station in a day. You need to find the minimum of platforms required for the railway station such that no ...read more

You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to return the list of all pairs of elements such that each sum of elements of each pair equals 'S'.

Note:

Each pair shou...read more

You are given an array of integers 'ARR' of length 'N' and an integer Target. Your task is to return all pairs of elements such that they add up to Target.

Note:

We cannot use the element at a given inde...read more

You have been given an array/list 'ARR' of integers. Your task is to find the second largest element present in the 'ARR'.

Note:

a) Duplicate elements may be present. b) If no...read more

Given a binary tree with N number of nodes, check if that input tree is BST (Binary Search Tree) or not. If yes, return true, return false otherwise.

A binary search tree (BST) is a binary tree data...read more

You are given an array of 'N' integers, and a positive integer 'K'. You need to determine if it is possible to divide the array into 'K' non-empty subsets such that the sum of el...read more

Ninja is now bored with numbers and is now playing with characters but hates when he gets repeated characters. Ninja is provided a string, and he wants to return the first unique ch...read more

You’re given a doubly-linked list with N nodes, where each node deviates at max K position from its position in the sorted list. Your task is to sort this given doubly linke...read more

You are given a Singly Linked List of integers and a positive integer 'K'. Modify the linked list by reversing every alternate 'K' nodes of the linked list.

A singly linked list is a ty...read more

You are given a string 'STR'. You have to convert the first alphabet of each word in a string to UPPER CASE.

For example:

If the given string 'STR' = ”I am a student of the third year” so you hav...read more

You are given a graph with ‘N’ nodes and ‘M’ unidirectional edges. Also you are given two integers ‘S’ and ‘D’ denoting the source and destination. Your task is to find all the paths from ‘S’ to...read more

You are given a non-empty binary tree where each node has a non-negative integer value. Return the maximum possible sum of path between any two leaves of the given tree.

The p...read more

You have been given stock values/prices for N number of days. Every i-th day signifies the price of a stock on that day. Your task is to find the maximum profit which you can make by buying and sel...read more

You are given a list of “N” strings A. Your task is to check whether you can form a given target string using a combination of one or more strings of A.

Note :

You can use any string of A multiple tim...read more

You are given two Strings 'P' and 'Q' of equal length. Your task is to check whether String 'P' can be converted into String 'Q' by cyclically rotating it to t...read more

Given 'K' sorted linked lists, each list is sorted in increasing order. You need to merge all these lists into one single sorted list. You need to return the head of the final linked list.

I...read more

Given a binary tree, return the zigzag level order traversal of the nodes' values of the given tree. Zigzag traversal means starting from left to right, then right to left for the ne...read more

You are given a 2-dimensional array/list having N rows and M columns, which is filled with ones(1) and zeroes(0). 1 signifies land, and 0 signifies water.

A cell is said to be connected to...read more

You have been given a linked list where each node has a single character. You have also been given a string 'STR'.

You have to remove all the occurrences of string STR from the linked list.

Note:

1...read more

You are given two strings 'A' and 'B' of words. Your task is to find out the most frequent and lexicographically smallest word in string 'A', which is not present in string 'B'. If no such wor...read more

How do we measure forty-five minutes using two identical wires, each of which takes an hour to burn? We have matchsticks with us. The wires burn non-uniformly. So, for example, the two halves of wire migh...read more

You are given an integer ‘N’ and there is a hidden number in the range [0, N] which you have to guess. You are also given a function higherLower(k) to help you in guessing the number. The ‘highe...read more

Given a singly linked list, you have to detect the loop and remove the loop from the linked list, if present. You have to make changes in the given linked list itself and return the update...read more

You have been given a long type array/list 'ARR' of size 'N'. It represents an elevation map wherein 'ARR[i]' denotes the elevation of the 'ith' bar. Print the total amount of rainwater that c...read more

You are given a Singly Linked List of integers. You need to reverse the Linked List by changing the links between nodes.

Input Format :

The first line of input contains a single integer T, re...read more

You are given a Singly Linked List of integers. Sort the Linked List using merge sort.

Merge Sort is a Divide and Conquer algorithm. It divides the input into two halves, calls itself for ...read more

You are given a string 'str' and an integer 'D'. Your task is to rotate the given string left (anticlockwise) and right (clockwise) by 'D' units from the starting index. You a...read more

You are given a string S of words. Your task is to find the number of palindrome words in the given string S. A word is called palindrome, if it reads the same backwards as for...read more

You have been given a square chessboard of size ‘N x N’. The position coordinates of the Knight and the position coordinates of the target are also given.

Your task is t...read more

You are given the root node of a binary tree consisting of ‘N’ nodes. Your task is to return its preorder traversal. The preorder traversal of a binary tree is defined as a process of traversi...read more

You have been given a binary tree, you are supposed to return the root values of all the duplicate subtrees. For each duplicate subtree, you only need to return the root value of any one of th...read more

Ninja is given an integer ‘N’. Ninja wants to find whether the binary representation of integer ‘N’ is palindrome or not.

A palindrome is a sequence of ch...read more

You are given an array ‘ARR’ of size ‘N,’ and you have to tell the minimum number of elements that need to be removed such that the array contains all distinct elements. More formally, there sh...read more

Sanyam has ‘N’ candies, he wants to distribute that into ‘K’ of his friends. He made his ‘K’ friends stand in line, in increasing order of his likeness. Not being so smart he ...read more

You are given two sorted arrays 'A' & 'B' of sizes 'N' & 'M'. You need to find the median of the two arrays when merged. If the total number of elements i.e., N + M is even then the m...read more

You have been given an integer array/list(ARR) of size N that contains only integers, 0 and 1. Write a function to sort this array/list. Think of a solution which scans the array/list only once and don'...read more

While practicing questions on data structures, Ninja faced a problem and was not able to pass all the test cases of a question as the time complexity of the code Ninja made was very large. Nin...read more

Ninja is given an integer ‘N’. Ninja wants to find whether the binary representation of integer ‘N’ is palindrome or not.

A palindrome is a sequence of characters that reads the same backward as...read more

You have been given a binary tree of 'N' nodes. Print the Spiral Order traversal of this binary tree.

For example

For the given binary tree [1, 2, 3, -1, -1, 4, 5, -1, -1,...read more

You have been given an integer array/list(arr) and a number 'Sum'. Find and return the total number of pairs in the array/list which when added, results equal to the 'Sum'.

Note:

G...read more

You are given two strings STR1 and STR2. You need to check whether STR2 can be formed from the characters of STR1. Both the strings can ...read more

Reverse a given stack of integers using recursion.

Note:

You are not allowed to use any extra space other than the internal stack space used due to recursion. You are not allowed to...read more

You are given ‘n’ carrots numbered from 1 to ‘n’. There are k rabbits. Rabbits can jump to carrots only with the multiples of Aj(Aj,2Aj,3Aj…) for all rabbits from 1 to k.

Whenever Rabbit reaches a c...read more

Given a string (STR) of length N, you have to create a new string by performing the following operation:

Take the smallest character from the first 'K' characters of STR, remove it from STR...read more

There is a wedding ceremony at NinjaLand. The bride and groom want everybody to play a game and thus, they have blindfolded the attendees. The people from the bride’s side are holding odd numb...read more

You are given two strings S and X containing random characters. Your task is to find the smallest substring in S which contains all the characters present in X.

Example:

Let S = “abdd” and X = “b...read more

Given a number ‘N', the task is to find the total number of derangements of a set of ‘N’ elements.

A ‘Derangement’ is a permutation of 'N' elements, such that no element appears in its origina...read more

Write a program to find the factorial of a number.

Factorial of n is:

n! = n * (n-1) * (n-2) * (n-3)....* 1

Output the factorial of 'n'. If it does not exist, output 'Error'.

Input format :...read more

Given an undirected and disconnected graph G(V, E), containing 'V' vertices and 'E' edges, the information about edges is given using 'GRAPH' matrix, where i-th edge is between GRAPH[i][0] and GRAP...read more