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Problem leetcode.com Solution This problem can be solve by DFS with depth of tree. In my code, lists.size() == depth means that the traversing depth changes. Source Code

Maximum Product of Word Lengths

Problem leetcode.com Solution This problem can be solved effectively by using bit manipulation. We can manage the count of appearance of each letters. Lower case letters are transformed to Integer within 26. This takes 0(N2) time. Source C…

Heaps: Find the Running Median

Problem www.hackerrank.com This problem is that we calculate median of array the range is from 0 to ith. Solution By using Two Priority Queues: minHeap and maxHeap, we can solve this problem. The roles of them are following. minHeap : To s…

Count Path Sum in Binary Tree

Problem You are given a binary tree in which each node contains an integer value. Find 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 fr…

Find an Element from Sorted Matrix

Problem Given an M * N matrix in which each row and each column is sorted in ascending order, write a method to find an element. Solution O(N + M) solution By traversing matrix from upper right to lower left, we can solve this problem in O…

Find the location of the given string from a sorted array of string which is interspersed with empty strings

Problem Given a sorted array of strings which is interspersed with empty strings, write a method to find the location of a given string EXAMPLE Input: find “ball” in {“at”, “”, “”, "ball”, "”, "”, "car”,“”, "”, "dad”, ”“, ”“} Output:4 Solu…

Print all paths which sum to a given value in a Binary Tree

Problem You are given a binary tree in which each node contains a value. Design an algorithm to print all paths which sum to a given value. The path dose not need to start or end at the root or leaf. Solution First, let’s approach this pro…

Check if small binary tree T1 is a suibtree of large binary Tree T2

Problem You have two large binary tree: T1, with millions of nodes, and T2, with hundreds of nodes. Create an algorithm to decide if T2 is a subtree of T1. A tree T2 is a subtree of T1 if there exists a node n in T1 such the the subtree of…

Find the next node (in-oder traversal) of a given node in a binary search tree

Problem Write an algorithm to find the next node (i.e., in-oder successor) of a given node in a binary search tree. You may assume that each node has a link to its parent. Solution This problem can be solved by thinking the two patterns. F…

Find the First Common Ancestor of the two nodes in a binary tree

Problem 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. Node: This is not necessarily a binary search tree. Solution I’ll solve this pr…

Check if a binary tree is a binary search tree

Problem Implement a function to check if a binary tree is a binary search tree Solution There are some solutions to solve this problem. I’ll introduce the all solution which includes I came up with. First Solution is using a range (min, ma…

Sorting the too large size data

Problem Imagine you have a 20 GB file with one string per line. Explain how you would sort the file. Solution When an interviewer gives a size limit of 20 gigabytes, it should tell you something. In this case, it suggests that they don’t w…

Internal Sorting and External Sorting

Kind of Sort All sort can be classified the following two sorts Internal Sorting External Sorting Imagine we have to sort the cards on the table where we can put the 30 cards(max). If the number of cards which we have to sort is less than …

Find an element in the rotated array

Problem Given a sorted array of n integers that has been rotated an unknown number of times, write code to find an element int the array. You may assume that the array was originally sorted in increasing order. Solution This problem can be…

Implement a Queue by using two Stacks

Problem Implement a MyQueue class which implements a queue using two stacks Source Code

Sort an array of strings by anagrams

Problem Write a method to sort an array of strings so that all the anagrams are next to each other. Solution This problem asks us to group the strings in arrays such that anagrams appear next to each other. How to find the anagram The feat…

Merge two sorted arrays

Problem You are given two sorted arrays, A and B, where A has large enough buffer at the end to hold B. Write a method to merge B into A in sorted order How to Solve By merging two arrays like merge sort, we can achieve the goal. Since A h…

Merge Sort and Quick Sort

Merge Sort Runtime: 0(n Log(n)) average and worst case. Quick Sort Runtime: 0(n Log(n)) average,0(n2) worst case.

Write a method to return all subsets of a set

Problem Write a method to return all subsets of a set Solution This problem can be solve by choosing each element or not. For example we given an array = {1, 2, 3}. First, we do the two patterns that we select 1 or not. By this operation, …

Find a Magic Index from Sorted Array

Problem A magic index in an array A[] is defined to be an index such that A[i] = i. Given a sorted array of distinct integers, write a method to find a magic index, if one exists, in array A. FOLLOW UP What if the values are not distinct? …

Robot is moving in grid

Problem Imagine a robot sitting on the upper left corner of an X by Y grid. The robot can only move in two directions: right and down. How many possible paths are there for the robot to go from (0, 0) to (X, Y)? How to Solve By using Dynam…

Count how many possible ways the child can run up the stairs

Problem A child is running up a staircase with n steps, and can hop either 1 step, 2 steps, or 3 steps at a time. Implement a method to count how many possible ways the child can run up the stairs. How to Solve This problem can be solved e…

Find the heavy bottle

Problem You have 20 bottles of pills. 19 bottles have 1.0 gram pills, but one has pills, but one has pills of weight 1.1 grams. Given a scale that provides an exact measurement, how would you find the heavy bottle? You can only use the sca…

Create a Linked List of all the nodes at each depth in Binary Tree

Problem Given a binary tree, design a 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) How to Solve The important point of the this problem How we shoul…

Make a Binary Search Tree from sorted array

Problem Given a sorted (increasing order) array with unique integer elements, write an algorithm to create a binary search tree with minimal height. How to Solve This problem asks me to create a BST (Binary Search Tree) from array. What is…

Find out whether there is a routes between two nodes

Problem Given a directed graph, design an algorithm to find out whether there is a route between two nodes. How to Solve This problem can be solved by depth first search or breadth first search. While traversing the graph, we have to contr…

Check if a binary tree is balanced

Problem Implement a function to check if a binary tree is balanced. For the purposes of this question. 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. How to Solve …

Towers of the Hanoi in Java

Problem In the classic problem of the Towers of Hanoi, you have 3 towers and N discs of different sizes which can slide onto any tower. How to Solve First we think about sliding nth disc onto another tower. This handling is composed by the…

Implement SetOfStacks

Problem Implement a data structure SetOfStacks. SetOfStacks should be composed of several stacks and should create a new stack once the previous one exceeds capacity. SetOfStacks.push() and .pop() should behave identically to a single stac…

Implement function min which returns minimum element in stack

Problem How would you design a stack which, in addition to push and pop, also has a function min which return minimum element? Push, pop and min should all operate in O(1) time. How to Solve By keeping a minimum value at each state, we can…

Use a single array to implement three stacks

Problem Describe how you could use a single array to implement three stacks. We can divide the array in three equal parts. So we use the array like this. For stack 1, we will use [0, n/3) For stack 2, we will use [n/3, 2n/3) For stack 3, w…

Implementation of Stack with LinkedList in Java

Implementation of Stack with LinkedList I defined the Stack class with a top property which is defined as the following explanation. top: the position to insert next Node at next time and the position to get a Node at next time. When I pus…

Implementation of Queue with LinkedList in Java

Implement Queue with LinkedList I defined a Queue class with the following two property, first and last. first: first it the position to dequeue at next time last: last.next is the position to enqueue at next time

Partition a Linked List around a value x

Problem Write code to partition a linked list around a value x, such that all nodes less than x come before all nodes larger than x or equal to x How to Solve First, I prepare two nodes that are beforeStart and afterStart. These nodes can …

Delete a Node in the middle of singly Linked List

Problem Implement an algorithm to delete a Node in the middle of singly Linked List, given only access to that Node example: in following linked list case ①→②→③→④→⑤ I'm given only node③ and I have to delete node③. Source Code

Find the kth to last element of singly Linked List

Problem Implement an algorithm to find the kth to last element of singly Linked List. How to Solve This problem can be solved by Recursive or normal traverse. In recursive case, we have to create IntWrapper Class and implement like this. B…

Remove Duplicates from an Linked List

Problem 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? How to Solve By using HashSet, I can control if each value appears or not already. And i…

Compress a String

Problem Implement a method to perform basic string compression using the counts of repeated characters. For example, the string aabcccccaaa would become a2b1c5a3. If the string would not become smaller than the original string, your method…

Replace all space in a string with '%20'

Problem Write a method to replace all space in a string with '%2d'. You may assume that the string has sufficient space at the end of the string to hold the additional character, and that you are given the true length of the string. [examp…

If the string is a permutation of another string

Problem Given two strings, write a method to decide if one is a permutation of the other. How to Solve In oder to count of the number that how many times each characters appeared, I use array like HashMap. In case the given strings is ASCI…

Implementation Reverse String Function

How to Implement By swapping the head of the string character and the tail of one, I can reverse a string

Determine if a string has all unique characters

Problem Implement an algorithm to determine if a string has all unique characters. What if you cannot use additional data structures. How to solve Character can be transformed into integer. So, by using array its size is 256(ASCII), we can…