Categories of Questions

## Array Questions CodeNation

**Count all subsequences having product less than K** The problem “Count all subsequences having product less than K” states that you are given an array of integers. Now find the number of subsequences that have a product less than a given input K. Example a[] = {1, 2, 3, 4, 5} k = 8 Number of subsequences less ...

**Range Queries for Longest Correct Bracket Subsequence** You are given a sequence of some brackets subsequence, in other words, you are given brackets like ‘(’ and ‘)’ and you are given a query range as a starting point and ending point. The problem “Range Queries for Longest Correct Bracket Subsequence” asks to find out the maximum length ...

**Longest Bitonic Subsequence** Suppose you have an array of integers, the problem statement asks to find out the longest bitonic subsequence. The bitonic sequence of an array is considered as the sequence which first increases and then decreases. Example arr[] = {1,4,2,76,43,78,54,32,1,56,23} 7 Explanation 1 ⇒ 4 ⇒ 76 ⇒ 78 ⇒ 54 ...

**Difference Array | Range update query in O(1)** You are given an integer array and two types of queries, one is to add a given number in a range and the other to print the whole array. The problem “Difference Array | Range update query in O(1)” requires us to perform the range updates in O(1). Example arr[] ...

**Painting Fence Algorithm** Problem Statement The “Painting Fence Algorithm” states that you are given a fence having some posts (some wooden pieces or some other pieces) and some colors. Find out the number of ways to paint the fence such that at most only 2 adjacent fences have the same color. Since this ...

**Constant time range add operation on an array** You have given an integer array and initially, it was initialized as 0 and also given a range. The task is to add the given number in the range of the array and print the resultant array. Example arr[] = {0, 0, 0, 0, 0} Query: {(0, 2, 50), (3, ...

**Number of elements less than or equal to a given number in a given subarray** Problem Statement The problem “Number of elements less than or equal to a given number in a given subarray” states that you are given an integer array and q number of queries. There will be two types of queries à queryUpdate(i, v): There will be two integers i and v, ...

**K maximum sums of overlapping contiguous sub-arrays** Problem Statement The problem “K maximum sums of overlapping contiguous sub-arrays” states that you are given an array of integers. Find the maximum sum of k-subarrays such that their sum is maximum. These k-subarrays might be overlapping. So, we need to find k-subarrays such that their sum is maximum among ...

**Maximum Subarray Sum Excluding Certain Elements** Problem Statement We are given an array, and we need to find maximum subarray sum excluding certain elements. That is, we need to find the max sum of subarray such that the subarray we are considering does not contain the elements which are told to be excluded. Example of maximum ...

**Largest rectangular sub-matrix whose sum is 0** Problem Statement Find the maximum size sub-matrix in a 2D array whose sum is zero. A sub-matrix is nothing but a 2D array inside of the given 2D array. So, you have a matrix of signed integers, you need to calculate the sum of sub-matrices and find the matrix with ...

**Matrix Chain Multiplication** In the matrix chain multiplication II problem, we have given the dimensions of matrices, find the order of their multiplication such that the number of operations involved in multiplication of all the matrices is minimized. Consider you have 3 matrices A, B, C of sizes a x b, b x ...

**Maximum Sum Increasing Subsequence** Problem Statement In the “Maximum Sum Increasing Subsequence” problem we have given an array. Find the sum of the maximum subsequence of the given array, that is the integers in the subsequence are in sorted order. A subsequence is a part of an array which is a sequence that is ...

## String Questions CodeNation

**Minimum insertions to form a palindrome with permutations allowed** The problem “Minimum insertions to form a palindrome with permutations allowed” states that you are given a String with all letters in lowercase. The problem statement asks to find out the minimum insertion of a character to a string that it can become Palindrome. The position of characters can be ...

**LCS (Longest Common Subsequence) of three strings** The problem “LCS (Longest Common Subsequence) of three strings” states that you are given 3 strings. Find out the longest common subsequence of these 3 strings. LCS is the string that is common among the 3 strings and is made of characters having the same order in all of the ...

**Maximum weight transformation of a given string** Problem Statement The maximum weight transformation of a given string problem states that given a string consisting only of two characters ‘A’ and ‘B’. We have an operation where we can transform string to another string by toggling any character. Thus many transformations are possible. Out of all the possible ...

**Backspace String Compare** In the backspace string compare problem we have given two Strings S and T, check if they are equal or not. Note that the strings contain ‘#’ which means backspace character. Examples Input S = “ab#c” T = “ad#c” Output true (as both S and T converts to “ac”) Input ...

**Check length of a String is Equal to the Number Appended at its Last** Problem Statement In the “Check length of a string is Equal to the Number Appended at its Last” problem we have given a string that is appended with a number at last. Write a program that checks whether the length of the string excluding the number is the same as ...

## Tree Questions CodeNation

**Number of elements less than or equal to a given number in a given subarray** Problem Statement The problem “Number of elements less than or equal to a given number in a given subarray” states that you are given an integer array and q number of queries. There will be two types of queries à queryUpdate(i, v): There will be two integers i and v, ...

**Red-Black Tree Introduction** Red Black Tree is a self-balancing binary tree. In this tree, every node is either a red node or a black node. In this Red-black Tree Introduction, we will try to cover all of its basic properties. Properties of Red-Black Tree Every node is represented as either red or black. ...

**Number of siblings of a given Node in n-ary Tree** Problem Statement The problem “Number of siblings of a given Node in n-ary Tree” states that you are given an n-ary Tree and a target node. Find the number of siblings of the target node. Assume that node is always present in the tree and the first node is the ...

**Segment Tree** If we have performing addition on a given range of array whose element values updated any time. Then in that type of problem, we handle using a segment tree structure. Given an array a[] with n elements and you have to answer multiple queries, each of the queries is one ...

## Stack Questions CodeNation

**Range Queries for Longest Correct Bracket Subsequence** You are given a sequence of some brackets subsequence, in other words, you are given brackets like ‘(’ and ‘)’ and you are given a query range as a starting point and ending point. The problem “Range Queries for Longest Correct Bracket Subsequence” asks to find out the maximum length ...

**Backspace String Compare** In the backspace string compare problem we have given two Strings S and T, check if they are equal or not. Note that the strings contain ‘#’ which means backspace character. Examples Input S = “ab#c” T = “ad#c” Output true (as both S and T converts to “ac”) Input ...

## Queue Questions CodeNation

**Number of siblings of a given Node in n-ary Tree** Problem Statement The problem “Number of siblings of a given Node in n-ary Tree” states that you are given an n-ary Tree and a target node. Find the number of siblings of the target node. Assume that node is always present in the tree and the first node is the ...

**Priority Queue** A priority queue is a type of data structure which is similar to a regular queue but has a priority associated with each of its element. Higher the priority earlier the element will be served. In some cases, there are two elements with the same priority then, the element enqueued ...

## Matrix Questions CodeNation

**Find maximum length Snake sequence** The problem “Find maximum length Snake sequence” states that we are provided with a grid containing integers. The task is to find a snake sequence with the maximum length. A sequence having adjacent numbers in the grid with an absolute difference of 1, is known as a Snake sequence. Adjacent ...

**Number of palindromic paths in a matrix** Problem Statement We are given a two-dimensional matrix containing lowercase English alphabets, we need to count the number of palindromic paths in it. A palindromic path is nothing but a path following palindromic property. A word which when reversed remains the same as the initial word is said to be ...

**Largest rectangular sub-matrix whose sum is 0** Problem Statement Find the maximum size sub-matrix in a 2D array whose sum is zero. A sub-matrix is nothing but a 2D array inside of the given 2D array. So, you have a matrix of signed integers, you need to calculate the sum of sub-matrices and find the matrix with ...

**Matrix Chain Multiplication** In the matrix chain multiplication II problem, we have given the dimensions of matrices, find the order of their multiplication such that the number of operations involved in multiplication of all the matrices is minimized. Consider you have 3 matrices A, B, C of sizes a x b, b x ...

## Other Questions CodeNation

**Sequences of given length where every element is more than or equal to twice of previous** The problem “Sequences of given length where every element is more than or equal to twice of previous” provides us with two integers m and n. Here m is the largest number that can exist in the sequence and n is the number of elements that must be present in the ...

**Count ways to reach the nth stair using step 1, 2 or 3** The problem “Count ways to reach the nth stair using step 1, 2, or 3” states that you are standing on the ground. Now you need to reach the end of the staircase. So how many ways are there to reach the end if you can jump only 1, 2, ...

**Maximum path sum in a triangle** Problem Statement The problem “Maximum path sum in a triangle” states that you are given some integers. These integers are arranged in the form of a triangle. You are starting from the top of the triangle and need to reach the bottom row. For doing this, you move to the ...

**The Painter’s Partition Problem** Problem Statement The Painter’s Partition problem states that we have some fences and we have some painters. We want to minimize the time of painting all the fences by painters. There is a bound on the order of painting the fences by painters. Consider we have n painters, then painter ...

**A Space Optimized DP solution for 0-1 Knapsack Problem** Problem Statement We are given a knapsack which can hold some weight, we need to pick some of the items out of given items with some value. The items should be picked such that the value of the knapsack ( total value of picked up items ) should be maximized. ...

**Longest Increasing Subsequence** We are provided with an array of integers that is unsorted and we have to find the longest increasing subsequence. The subsequence need not be consecutive The subsequence shall be increasing Let’s understand that better by a few examples. Example Input [9, 2, 5, 3, 7, 10, 8] Output 4 ...