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.

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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.

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Given two binary trees, merge them into a new binary tree such that if two nodes overlap then add them and put them into the new tree at the same location else put the non-NULL node in the new tree.

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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.

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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.

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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.

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Given an array X[] of distinct elements, write a program to find all the unique triplets in the array whose sum is equal to zero.

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Write a program to implement a stack using the queues. The implemented stack should support standard operations like push(x), pop(), and top(). This is an excellent problem to learn problem-solving and visualize the use case of stack and queue operations.

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Write a program to Implement a queue using the stack. The implemented queue should support standard operations like enqueue, dequeue, and front. This is an excellent problem to learn problem-solving and visualize the use case of stack and queue operations.

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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.

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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.

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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.

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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!

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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If we want to make a change for a given value K of cents, and we have an infinite supply of each of coin[ ] = [C1, C2, …, Cm] valued coins, write a program to find the minimum number of coins required to make the change?

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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.

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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.

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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.

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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.

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

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Given an unsorted array X[] consisting of n integers, we need to write a program to find the length of the longest consecutive sequence of integers in the array. The consecutive numbers can be in any order.

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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.

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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.

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

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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.

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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.

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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.

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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.

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Given an array X[] with n elements, we need to write a program to find the maximum subarray sum among all subarrays. 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.

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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.

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

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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. Moreover, the algorithm for binary search also helps us to solve several coding problems.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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