Salvatore Labs

LeetCode

28. Find the Index of the First Occurrence in a String

The Problem Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Examples Example 1: Input: haystack = "sadbutsad", needle = "sad" Output: 0 Explanation: "sad" occurs at index 0

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LeetCode: 14. Longest Common Prefix

The Problem Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "". Examples Example 1: Input: strs = ["flower","flow","flight"] Output: "fl" Example 2: Input:

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LeetCode: 58. Length of Last Word

The Problem Given a string s consisting of words and spaces, return the length of the last word in the string. A word is a maximal substring consisting of non-space characters only. Example Example 1: Input: s = "Hello World" Output: 5 Explanation: The last word is "World&

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LeetCode: 13. Roman to Integer

The Problem Roman numerals are represented by seven different symbols: I, V, X, L, C, D and M. Symbol       ValueI             1 V             5 X             10 L             50 C             100 D             500 M             1000 For example, 2 is written as II in Roman numeral, just two ones added together. 12 is

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LeetCode: 121. Best Time to Buy and Sell Stock

The Problem You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return

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LeetCode: 169. Majority Element

The Problem Given an array nums of size n, return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example Example 1: Input: nums = [3,2,3] Output: 3 Example 2:

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LeetCode: 26. Remove Duplicates from Sorted Array

The Problem Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of

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LeetCode: 27. Remove Element

The Problem Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are

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LeetCode: 88. Merge Sorted Array

The Problem You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be

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LeetCode: 69. Sqrt(x)

The Problem Given a non-negative integer x, return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. * For example, do not use pow(x, 0.5) in c++ or x

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LeetCode: 437. Path Sum III

The Problem Given the root of a binary tree and an integer targetSum, return the number of paths where the sum of the values along the path equals targetSum. The path does not need to start or end at the root or a leaf, but it must go downwards (i.

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LeetCode: 337. House Robber III

The Problem The thief has found himself a new place for his thievery again. There is only one entrance to this area, called root. Besides the root, each house has one and only one parent house. After a tour, the smart thief realized that all houses in this place form

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LeetCode: 331. Verify Preorder Serialization of a Binary Tree

The Problem One way to serialize a binary tree is to use preorder traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as '#'. Example The above binary tree can be

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LeetCode: 236. Lowest Common Ancestor of a Binary Tree

The Problem Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and

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LeetCode: 235. Lowest Common Ancestor of a Binary Search Tree

The Problem Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has

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LeetCode: 230. Kth Smallest Element in a BST

The Problem Given the root of a binary search tree, and an integer k, return thekthsmallest value (1-indexed) of all the values of the nodes in the tree. Example Input: [3,1,4,null,2], k = 1 Output: 1 Constraints: * The number of nodes in the tree is n. * 1

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LeetCode: 199. Binary Tree Right Side View

The Problem Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom. Example Input: root = [1,2,3,null,5,null,4] Output: [1,3,4] Solution We opted for

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LeetCode: 173. Binary Search Tree Iterator

The Problem Implement the BSTIterator class that represents an iterator over the in-order traversal of a binary search tree (BST): * BSTIterator(TreeNode root) Initializes an object of the BSTIterator class. The root of the BST is given as part of the constructor. The pointer should be initialized to a non-existent

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LeetCode: 129. Sum Root to Leaf Numbers

The Problem You are given the root of a binary tree containing digits from 0 to 9 only. Each root-to-leaf path in the tree represents a number. For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123. Return the total sum of all root-to-leaf

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LeetCode: 117. Populating Next Right Pointers in Each Node II

The Problem Given a binary tree struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL. Initially, all next pointers are set to NULL.

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LeetCode: 116. Populating Next Right Pointers in Each Node

The Problem You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right

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LeetCode: 114. Flatten Binary Tree to Linked List

The Problem Given the root of a binary tree, flatten the tree into a "linked list": * The "linked list" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null.

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LeetCode: 113. Path Sum II

The Problem Given the root of a binary tree and an integer targetSum, return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values, not node references. A root-to-leaf path is a path

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LeetCode: 109. Convert Sorted List to Binary Search Tree

The Problem Given the head of a singly linked list where elements are sorted in ascending order, convert it to a height-balanced binary search tree. Input: head = [-10,-3,0,5,9] Output: [0,-3,9,-10,null,5] Explanation: One possible answer is [0,-3,9,-10,null,5]

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LeetCode: 107. Binary Tree Level Order Traversal II

The Problem Given the root of a binary tree, return the bottom-up level order traversal of its nodes' values. (i.e., from left to right, level by level from leaf to root). Example Input: [3,9,20,null,null,15,7] Output: [[15,7],[9,20],[3]] Constraints: * The