All content related to coding-interview-questions

Find Leaders in an Array

Given an integer array X[] of size n, write a program to find all the leaders in the array X[]. An element is a leader if it is strictly greater than all the elements to its right side.

Find k'th largest element in a BST

Given the root of a binary search tree and an integer k, write a program to return the kth largest value of all the values of the nodes in the tree.

Minimum absolute difference in BST

Given the root of a Binary Search Tree (BST), write a program to return the absolute minimum difference between the values of any two nodes in the tree.

Max Consecutive Ones

An input binary array X[] is given where all the elements are either 0 or 1. Write a program to find the maximum consecutive ones in this binary array.

Product of Array Except Self

Given an array X[] of n integers, write a program to return an array product[] such that product[i] is equal to the product of all the elements of X except X[i].

Sort Characters by Frequency

Given a string S, write a program to sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string.

Find the Intersection of Two Unsorted Arrays

Given two integer arrays X[] and Y[] of size m and n, respectively, write a program to find the intersection of these two arrays. The intersection of two arrays is a list of distinct numbers which are present in both arrays. The numbers in the intersection can be in any order.

Find the Length of the Largest Subarray with Zero Sum

Given an array X[] of n integer elements, write a program to find the length of the longest subarray with a sum equal to 0. In general, for all j > i, find **max (j - i + 1)** among all subarray with zero-sum. Note: the length of a subarray starting from index i and ending at index j = j - i + 1.

Find the Maximum Depth or Height of a Tree

Given a binary tree, write a program to find the height of it. A binary tree's height or depth is the total number of nodes or edges on the longest path from the root node to the leaf node.

Max Continuous Series of 1s

You are given an array of 1s and 0s and you are given an integer k which signifies the number of flips allowed. Write a program to find the position of zeros which when flipped will produce maximum continuous series of 1s.This is one of the good problems to understand the idea of the sliding window technique. Using this approach, We can solve several interview problems efficiently in O(n) and O(1) space.

Find the maximum j – i such that A[j] > A[i]

Given an unsorted array X[] of distinct elements, write a program to find the maximum j  -  i such that j > i and X[j] > X[i].

Intersection of two Sorted Linked Lists

Given two sorted linked lists, write a program to find the intersections of the linked lists, and return the head of the new Linked List.

Find middle node of a linked list

Given a singly linked list, write a program to find the middle node of the linked list. If the node count is even then we need to return the second middle node.

Find Min Depth of a Binary Tree

Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. The path has to end on a leaf node.

Check if two arrays are equal or not

Given two integer arrays X[] and Y[], write a program to check if the arrays are equal or not. Two arrays are equal if they have the same elements in any order. If there are repeated elements, then counts of repeated elements must also be the same for both arrays.

Counting Sort

The counting sort algorithm assumes that each n input element is an integer in the range 0 to k. So by using array indexing as a tool for determining relative order, counting sort can sort n numbers in O(k + n) time when k = O(n). In other words, counting sort is one of the popular linear time sorting algorithms that works in O(n) time complexity if input elements are an integer in the range 0 to k.

Longest Common Subsequence

The longest common subsequence algorithm is a problem to find the length of the longest subsequence common to all subsequences of two strings. The lcs algorithm differs from the algorithm of the longest common substring problem. Explore and Enjoy!

Find next greater elements in an array

Given an array, find the next greater element for every element in the array. The next greater element for an element is the first greater element on the right side of the array. This is one of the best problems to learn problem-solving using stack.

Minimum number of Jumps to reach End

An array of non-negative integers is given and the aim is to reach the last index in the minimum number of jumps. You are initially positioned at the first index of the array and each element in the array represents your maximum jump length at that position.

Roman to Integer

Given a Roman numeral, write a program to find its corresponding decimal value. Roman numerals are represented by seven different symbols: I , V, X, L, C, D and M.

Remove Nth Node from List End

Write a program to remove the Nth node from the end of the linked list i.e. when the node is traversed from the end we have to delete the Nth node from there.

Find all possible combinations of K numbers from 1 to n

Given two numbers n and K and you have to find all possible combinations of K numbers from 1 to n. This is a good interview problem to understand the concept of problem-solving using backtracking and combinatorics.

Loop in a Linked List

Write a program to detect the loop in a linked list. A linked list with a cycle causes iteration over the list to fail because the iteration will never reach the end of the list. Therefore, it is desirable to be able to detect that a linked list has no cycle before trying an iteration. So, we are going to discuss various algorithms to detect a loop in a singly linked list. This is also one of the best-linked list interview problems.

Reversing a Linked List

Write a program to reverse a linked list. A head pointer of a linked list is given and our task to reverse the entire list so that when the resulted list is traversed it looks like we are traversing the original list from tail to head.

Minimum Coin Change

If we want to make a change for a given value K of cents, and we have an infinite supply of each of coin[ ] = [C​1​​, C​2​​, …, C​m​​] valued coins, write a program to find the minimum number of coins required to make the change?

Median of two sorted arrays of the equal size

There are two sorted arrays A and B of size n each, write a program to find the median of the array obtained after merging both the arrays(i.e., an array of length 2n which is even). The median of a sorted array of size n is defined as the middle element when n is odd and the average of the middle two elements when n is even.

Climbing Stairs Problem

There is a staircase of n steps and you can climb either 1 or 2 steps at a time. You need to count and return the total number of unique ways to climb the staircase. The order of steps taken matters.

Longest Substring Without Repeating Characters

Write a program to find the length of the longest substring without repeating characters. Substring is the continuous sub-part of the string. The aim is to determine the maximum such subpart which has all the unique characters.

The maximum difference between two elements

Given an array A[] of integers, find out the maximum difference between any two elements such that the larger element appears after, the smaller element. In other words, we need to find max(A[j] - A[i]), where A[j] > A[i] and j > i.

First Missing Positive

Given an array that includes both positive and negative numbers, write a program to find the first missing positive integer.

Longest Consecutive Sequence

Given an array X[] of n integers, write a program to find the length of the longest consecutive elements sequence. In other words, we need to find the length of the longest sub-sequence such that elements in the subsequence are consecutive integers. The consecutive numbers can be in any order.

Print a given matrix in spiral order

Given a 2-dimensional matrix, print the elements in spiral order. This is a good matrix problem to understand problem solving using both iteration and recursion.

Find most frequent element in an array

Given an array X[] of size n, write a program to find the most frequent element in the array, i.e. the element which occurs the most number of times. It is assumed that at least one element is repeated.

Find the row with the maximum number of 1s

Given a boolean 2D array, where each row is sorted. Find the row with the maximum number of 1s. This is an excellent matrix problem that can be solved in linear time complexity. The best part is — we are using the sorted order property and nested loops to improve the solution over the binary search approach.

Find whether an array is a subset of another array

We are given two integer arrays X[] and Y[], write a program to check whether array Y[] is a subset of array X[] or not. An array Y is a subset of another array X if each Y element is present in X. How do you check if one array is a subset of another? Explore and Enjoy!

Find the maximum in an array which is first increasing and then decreasing

You are given an array of integers that is initially increasing and then decreasing, find the maximum value in the array.

Find first and last positions of an element in a sorted array

Given an array of integers sorted in ascending order, find the first and last position of a given value. This is a good interview problem to learn problem-solving using binary search.

Iterative Binary Tree Traversal using Stack: Preorder, Inorder and Postorder

In recursive DFS traversals of a binary tree, we have three basic elements to traverse— root, left subtree, and right subtree. The traversal order depends on the order in which we process the root node. Here recursive code is simple and easy to visualize — only one function parameter and 3–4 lines of code. So critical question would be — How can we convert it into iterative code using stack? To simulate the recursive traversal into an iterative traversal, we need to understand the flow of recursive calls.

Level Order Traversal of a Binary Tree :  Breadth First Search

Level order traversal accesses nodes in level by level order. This is also called breadth-first search traversal or BFS traversal. Here we start from the root node and process it, then process all the nodes at the first level, then process all the nodes at the second level, and so on. In other words, we explore all nodes at the current level before moving on to the nodes at the next level.

kth smallest element in an array

Given an array and a positive integer k, write a program to find the kth smallest element in the array. One of the famous problems to learn a quick-select approach that helps optimize time complexity to O(n) average.

Majority element in an array

You are given an array X[] consisting of n elements, write a program to find majority element in an array i..e return the number which appears more than n/2 times. You may assume that the array is non-empty and the majority element always exists in the array. A majority element is an element that appears more than n/2 times, so there is at most one such element.

Search in a row-wise sorted 2D matrix

You are given a row-wise sorted 2D matrix and a given integer k, write a program to find whether the integer ‘k’ is present in the matrix or not. The matrix has the following properties: Integers in each row are sorted from left to right and the first integer of each row is greater than the last integer of the previous row.

Maximum Subarray Sum

Given an array X[] with n elements, we need to write a program to find the largest contiguous subarray sum. A subarray of array X[] of length n is a contiguous segment from X[i] through X[j] where 0<= i <= j <= n. Kadane algorithm idea is intuitive, using a single loop and few variables to solve the problem. We can use a similar idea to solve other coding problems.

Check for pair in an array with a given sum

Given an array of n integers and a target number, write a program to check whether a pair sum exits in the array or not. In other words, we need to check whether pair of elements in the array sum exactly to the target value.

Rotate a matrix by 90 degrees in an anticlockwise direction

Given an n x n 2D matrix representing an image, rotate the image by 90 degrees in an anticlockwise direction.

n Repeated element in 2n size array

In an array of size 2n, there are n+1 unique elements, and exactly one of these elements is repeated n times. Return the element repeated n times.

Binary Search Algorithm: Fast Searching on Sorted Array!

The binary search is one of the fastest search algorithms, which searches a value in the sorted array in an O(logn) time complexity. Here we search a value using divide and conquer by repeatedly dividing the search interval in half. Problem statement: Given a sorted array X[] of n elements, search a given element key in X[]. If the key exists, then return its index in the sorted array. Otherwise, return -1.

Quicksort: one of the fastest sorting algorithms!

Quicksort is often the best practical choice for sorting because it works remarkably efficiently on average O(nlogn) time complexity. It is also one of the best algorithms to learn problem-solving using recursion and divide and conquer approach. In this blog, we have covered: 1) How quick sort works recursively? 2) Choosing a correct pivot value in the partition algorithm 3) Best, worst, and average-case time complexity analysis 4) Space complexity and essential properties of the quick sort. Explore and Enjoy!

Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining. This is a famous rainwater trapping problem.

Remove duplicates from sorted array

Write a program to remove the duplicates from the sorted array. For this we are given a sorted array, the task is to remove the duplicate elements such that there is a single occurrence of each element in the array.

Container With Most Water

Given an array of n non-negative integers height[n], where each represents a point at coordinate (i, height[i]). n vertical lines are drawn such that the two endpoints of line i is at (i, height[i]) and (i, 0).  Write a program to find two lines, which together with the x-axis forms a container, such that the container contains the most water.

Sort an array of 0s, 1s, and 2s —Dutch National Flag Problem

Given an array a[] consisting of 0s, 1s, and 2s. Write a program to sort the array of 0’s, 1’s, and 2’s in ascending order. This is a famous coding interview problem asked in facebook, microsoft and amazon.

Valid Mountain Array

Given an array X[] of n integers, return true if and only if it is a valid mountain array. The array X[] is a mountain array if and only if n >= 3 and there exists some i with 0 < i < n - 1 such that: X[0] < X[1] <...X[i-1] < X[i] and X[i] > X[i+1] > ...> X[n - 1]. In other words, we call the array mountain array when the array is strictly increasing and then strictly decreasing.

Sort an array in a waveform

Given an array of integers, sort the array into a wave-like arrangement. In other words, An array A[0..n-1] is sorted in wave form if A[0] >= A[1] <= A[2] >= A[3] <= A[4] >= ….This problem has been asked during google coding interview.

Find the minimum and maximum value in an array

Given an array X[] of size n, we need to find the maximum and minimum element present in the array. This coding problem has been asked during facebook and microsoft interview.

Move Zeroes to End of an Array

Given an array X[] of n elements filled with several integers, some of them being zeroes, write a program to move all the zeroes to the end. This is an excellent coding problem to learn space and time complexity optimization.

Merge Sort Algorithm

Merge sort is one of the fastest comparison-based sorting algorithms, which works on the principle of the divide and conquer approach. The worst and best case time complexity of merge sort is O(nlogn), and space complexity is O(n). It is also the best algorithm for sorting linked lists.

Find equilibrium index of an array

Write a program to find the equilibrium index of an array. An array's equilibrium index is an index such that sum of elements at lower indexes equal to the sum of elements at higher indexes. This is an excellent coding question to learn — how to optimize space complexity and solve the problem using a single scan.

Why should we learn data structures and algorithms?

There are four critical importance to learn data structures and algorithms: 1) An algorithm is a technology 2) It is at the core of library functions and several APIs 3) For cracking the coding interview 4) Algorithms are beautiful! This blog answer one of the critical questions: how do we develop a long-term motivation to learn data structures and algorithms?

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