Algorithms

An exposition of coding problems and solutions. For each problem listed here, you can follow the link to find my solutions. Credit due to Leet code, Code Wars, and Cracking the Coding Interview for providing great algorithms to work through.

Algorithm Topics

• Trees
• Stacks and Queues
• Linked Lists
• String and Array Manipulation

Trees

Binary Tree Level Order Traversal

From LeetCode

"Given a binary tree, return the level order traversal of its nodes' values."

JavaScript Solution

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Convert Sorted Array to Binary Search Tree

From LeetCode

"Given an array where elements are sorted in ascending order, convert it to a height balanced BST."

JavaScript Solution

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Binary Tree Cousins

From LeetCode

"Given a binary tree and two unique values, check if two nodes with those values are cousins (same level with different parents)."

JavaScript Solution

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Convert BST to Greater Tree

From LeetCode

"Given a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST."

JavaScript Solution

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Subtree of Another Tree

From LeetCode

"Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants."

JavaScript Solution

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Binary Tree Tilt

From LeetCode

"Given a binary tree return the tilt of the tree, which is the absolute value of the difference between left and right values."

JavaScript Solution

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Balanced Binary Tree

From LeetCode

"Given a binary tree, determine if it is height-balanced, where the left and right subtrees of every node differ in height by no more than 1."

JavaScript Solution

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Symmetric Tree

From LeetCode

"Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center)."

JavaScript Solution

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Stacks and Queues

Towers of Hanoi

Modified From Cracking the Coding Interview

Write a function that solves the Towers of Hanoi problem using three stacks.

JavaScript Solution

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Stack with Min

Modified From Cracking the Coding Interview

Create a Stack class which also has a function min that returns the minimum element. Functions push, pop, and min should all operate in O(1) time.

JavaScript Solution

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Linked Lists

Sum Linked List Digits

From Cracking the Coding Interview

Write a function that add two linked lists together, where each node contains a single digit stored in reverse order.

JavaScript Solution

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Linked List Cycle

"Given a linked list, determine if it has a cycle in it."

JavaScript Solution

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Reverse Linked List

From LeetCode

"Reverse a singly linked list."

JavaScript Solution

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Linked List Midpoint

"Find the midpoint of a singly linked list."

JavaScript Solution

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Partition Linked List

From Cracking the Coding Interview

"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."

JavaScript Solution

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K to Last Value of a Linked List

From Cracking the Coding Interview

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

JavaScript Solution

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Remove Given Node from a Linked List

From Cracking the Coding Interview

"Implement an algorithm to delete a node in the middle of a singly linked list, given only access to that node."

JavaScript Solution

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Remove Duplicates from a Linked List

Modified From Cracking the Coding Interview

"Write code to remove duplicated from an unsorted, singly linked list."

JavaScript Solution

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String and Array Manipulation

Validate Sudoku

From LeetCode

"Determine if a 9x9 Sudoku board is valid."

JavaScript Solution

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String Permutation

From Cracking the Coding Interview

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

JavaScript Solution

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Two Sum

From LeetCode

"Given an array of integers, return indices of the two numbers such that they add up to a specific target."

JavaScript Solution

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String Compression

Modified From Cracking the Coding Interview

"Implement a method to perform basic string compression using the counts of repeated characters."

JavaScript Solution

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Unique String

From Cracking the Coding Interview

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

JavaScript Solution

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Sum of Digits / Digital Root

From Code Wars

"A digital root is the recursive sum of all the digits in a number. Given n, take the sum of the digits of n. If that value has more than one digit, continue reducing in this way until a single-digit number is produced. This is only applicable to the natural numbers."

Ruby Solution

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Growth of a Population

From Code Wars

"In a small town the population is p0 = 1000 at the beginning of a year. The population regularly increases by 2 percent per year and moreover 50 new inhabitants per year come to live in the town. How many years does the town need to see its population greater or equal to p = 1200 inhabitants?"

JavaScript Solution