Interview Qs

Animal Shelter: An animal shelter, which holds only dogs and cats, operates on a strictly"first in, first out" basis. People must adopt either the "oldest" (based on arrival time) of all animals at the shelter, or they can select whether they would prefer a dog or a cat (and will receive the oldest animal of that type). They cannot select which specific animal they would like. Create the data structures to maintain this system and implement operations such as enqueue, dequeueAny, dequeueDog, and dequeueCat. You may use the built-in Linked list data structure.

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Assumeyou have a method isSubstringwhich checks if oneword is a substring of another. Given two strings, sl and s2, write code to check if s2 is a rotation of sl using only one call to isSubstring (e.g., "waterbottle" is a rotation of"erbottlewat").

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BST Sequences: A binary search tree was created by traversing through an array from left to right and inserting each element. Given a binary search tree with distinct elements, print all possible arrays that could have led to this tree. EXAMPLE Input: Output: {2, 1, 3}, {2, 3, 1}

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Binary to String: Given a real number between O and 1 (e.g., 0.72) that is passed in as a double, print the binary representation. If the number cannot be represented accurately in binary with at most 32 characters, print "ERROR:'

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Build Order: You are given a list of projects and a list of dependencies (which is a list of pairs of projects, where the second project is dependent on the first project). All of a project's dependencies must be built before the project is. Find a build order that will allow the projects to be built. If there is no valid build order, return an error. EXAMPLE Input: projects: a, b, c, d, e, f dependencies: (a, d), (f, b), (b, d), (f, a), (d, c) Output: f, e, a, b, d, c Hints: #26, #47, #60, #85, #725, #133

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Check Balanced: Implement a function to check if a binary tree is balanced. For the purposes of this question, a balanced tree is defined to be a tree such that the heights of the two subtrees of any node never differ by more than one.

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Check Subtree: Tl and T2 are two very large binary trees, with Tl much bigger than T2. Create an algorithm to determine if T2 is a subtree of Tl. A tree T2 is a subtree of Tl if there exists a node n in Tl such that the subtree of n is identical to T2. That is, if you cut off the tree at node n, the two trees would be identical.

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Conversion: Write a function to determine the number of bits you would need to flip to convert integer A to integer B. EXAMPLE Input: 29 (or: 11101), 15 (or: 01111) Output: 2 Hints: #336, #369

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Debugger: Explain what the following code does: ( ( n & ( n-1)) == 0). Hints:#757,#202,#267,#302,#346,#372,#383,#398 ...

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Draw Line: A monochrome screen is stored as a single array of bytes, allowing eight consecutive pixels to be stored in one byte. The screen has width w, where w is divisible by 8 (that is, no byte will be split across rows). The height of the screen, of course, can be derived from the length of the array and the width. Implement a function that draws a horizontal line from ( xl, y) to ( x2, y). The method signature should look something like: drawline(byte[] screen, int width, int xl, int x2, int y)

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First Common Ancestor: Design an algorithm and write code to find the first common ancestor of two nodes in a binary tree. Avoid storing additional nodes in a data structure. NOTE: This is not necessarily a binary search tree. Hints: #70, #76, #28, #36, #46, #70, #80, #96

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Flip Bit to Win: You have an integer and you can flip exactly one bit from a 0 to a 1. Write code to find the length of the longest sequence of ls you could create. EXAMPLE Input: 1775 Output: 8 (or: 11011101111) Hints: #759, #226, #374, #352

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Given a string, write a function to check if it is a permutation of a palindrome. A palindrome is a word or phrase that is the same forwards and backwards. A permutation is a rearrangement of letters. The palindrome does not need to be limited to just dictionary words.

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Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

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Given two strings, write a method to decide if one is a permutation of the other.

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Implement a function to check if a linked list is a palindrome.

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Implement a method to perform basic string compression using the counts of repeated characters. For example, the string aabcccccaaa would become a2blc5a3. If the "compressed" string would not become smaller than the original string, your method should return the original string. You can assume the string has only uppercase and lowercase letters (a - z).

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Implement an algorithm to delete a node in the middle (i.e., any node but the first and last node, not necessarily the exact middle) of a singly linked list, given only access to that node. EXAMPLE lnput:the node c from the linked lista->b->c->d->e->f Result: nothing is returned, but the new linked list looks like a->b->d->e->f

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Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures?

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Implement an algorithm to find the kth to last element of a singly linked list.

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Insertion: You are given two 32-bit numbers, N and M, and two bit positions, i and j. Write a method to insert M into N such that M starts at bit j and ends at bit i. You can assume that the bits j through i have enough space to fit all of M. That is, if M = 10011, you can assume that there are at least 5 bits between j and i. You would not, for example, have j = 3 and i = 2, because M could not fully fit between bit 3 and bit 2. EXAMPLE Input: N 10000000000, M Output: N = 10001001100

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Intersection: Given two (singly) linked lists, determine if the two lists intersect. Return the intersecting node. Note that the intersection is defined based on reference, not value. That is, if the kth node of the first linked list is the exact same node (by reference) as the jth node of the second linked list, then they are intersecting. Hints:#20, #45, #55, #65, #76, #93, #111, #120, #129

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List of Depths: Given a binary tree, design an algorithm which creates a linked list of all the nodes at each depth (e.g., if you have a tree with depth D, you'll have D linked lists).

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Minimal Tree: Given a sorted (increasing order) array with unique integer elements, write an algorithm to create a binary search tree with minimal height.

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Next Number: Given a positive integer, print the next smallest and the next largest number that have the same number of 1 bits in their binary representation. Hints: #747, #7 75, #242, #372, #339, #358, #375,

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Pairwise Swap: Write a program to swap odd and even bits in an integer with as few instructions as possible (e.g., bit 0 and bit 1 are swapped, bit 2 and bit 3 are swapped, and so on). Hints: #745, #248, #328, #355

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Paths with Sum: You are given a binary tree in which each node contains an integer value (which might be positive or negative). Design an algorithm to count the number of paths that sum to a given value. The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes). Hints:#6, #14, #52, #68, #77, #87, #94, #103, #108, #115

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Queue via Stacks: Implement a MyQueue class which implements a queue using two stacks.

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Random Node: You are implementing a binary tree class from scratch which, in addition to insert, find, and delete, has a method getRandomNode() which returns a random node from the tree. All nodes should be equally likely to be chosen. Design and implement an algorithm for getRandomNode, and explain how you would implement the rest of the methods.

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Route Between Nodes: Given a directed graph, design an algorithm to find out whether there is a route between two nodes.

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Sort Stack: Write a program to sort a stack such that the smallest items are on the top. You can use an additional temporary stack, but you may not copy the elements into any other data structure (such as an array). The stack supports the following operations: push, pop, peek, and is Empty.

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Stack Min: How would you design a stack which, in addition to push and pop, has a function min which returns the minimum element? Push, pop and min should all operate in 0(1) time. Hints:#27, #59, #78

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Stack of Plates: Imagine a (literal) stack of plates. If the stack gets too high, it might topple. Therefore, in real life, we would likely start a new stack when the previous stack exceeds some threshold. Implement a data structure SetOfStacks that mimics this. SetO-fStacks should be composed of several stacks and should create a new stack once the previous one exceeds capacity. SetOfStacks. push() and SetOfStacks. pop() should behave identically to a single stack (that is, pop () should return the same values as it would if there were just a single stack). FOLLOW UP Implement a function popAt ( int index) which performs a pop operation on a specific sub-stack.

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Successor: Write an algorithm to find the "next" node (i.e., in-order successor) of a given node in a binary search tree. You may assume that each node has a link to its parent.

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Sum Lists: You have two numbers represented by a linked list, where each node contains a single digit. The digits are stored in reverse order, such that the 1 's digit is at the head of the list. Write a function that adds the two numbers and returns the sum as a linked list. EXAMPLE Input: (7-> 1 -> 6) + (5 -> 9 -> 2).That is,617 + 295. Output: 2 -> 1 -> 9. That is, 912. FOLLOW UP Suppose the digits are stored in forward order. Repeat the above problem. EXAMPLE lnput:(6 -> 1 -> 7) + (2 -> 9 -> 5).That is,617 + 295. Output: 9 -> 1 -> 2. That is, 912.

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There are three types of edits that can be performed on strings: insert a character, remove a character, or replace a character. Given two strings, write a function to check if they are one edit (or zero edits) away.

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Three in One: Describe how you could use a single array to implement three stacks. Hints: #2, #72, #38, #58

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Validate BST: Implement a function to check if a binary tree is a binary search tree.

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Write a method to replace all spaces in a string with '%20'. You may assume that the string has sufficient space at the end to hold the additional characters, and that you are given the "true" length of the string. (Note: If implementing in Java, please use a character array so that you can perform this operation in place.)

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Write an algorithm such that if an element in an MxN matrix is 0, its entire row and column are set to 0.

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Write code to partition a linked list around a value x, such that all nodes less than x come before all nodes greater than or equal to x. If x is contained within the list, the values of x only need to be after the elements less than x (see below). The partition element x can appear anywhere in the "right partition"; it does not need to appear between the left and right partitions. EXAMPLE Input: Output: 3 -> 5 -> 8 -> 5 -> 10 -> 2 -> 1 [partition= 5] 3 -> 1 -> 2 -> 10 -> 5 -> 5 -> 8

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Write code to remove duplicates from an unsorted linked list. FOLLOW UP How would you solve this problem if a temporary buffer is not allowed?

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