Hash Table

ProblemDetermine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned r ...

ProblemGiven a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. 12345class Node { public int val; public List<Node> neighbors;} Test case format: For simplicity, each node’s value is the same as the node’s index (1-indexed). For example, the first node with val == 1, the second node with val == 2, and so on. The graph is represented in the te ...

ProblemGiven two strings s and t, determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character, but a character may map to itself. Example 1: Input: s = “egg”, t = “add” Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a ...

ProblemGiven two strings ransomNote and magazine, return true if ransomNote can be constructed by using the letters from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: 123Input: ransomNote = "a", magazine = "b"Output: false Example 2: 12Input: ransomNote = "aa", magazine = "ab"Output: false Example 3: 123Input: ransomNote = "aa", magazine = "aab"Output: true Constraints: 1 <= ...

ProblemImplement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present, false otherwise. int getRandom() Returns a random element from the current set of elements (it’s guaranteed that at least one element exists when this method is called). ...

ProblemGiven 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 1: 123Input: nums = [3,2,3]Output: 3 Example 2: 123Input: nums = [2,2,1,1,1,2,2]Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in 1O(1) space? Solve解112345678910class Solutio ...

ProblemGiven two strings s and t of lengths m and n respectively, return the minimum window substring of 1s such that every character in 1t (including duplicates) is included in the window . If there is no such substring, return the empty string 1"" . The testcases will be generated such that the answer is unique. Example 1: 1234Input: s = "ADOBECODEBANC", t = "ABC"Output: "BANC"Explanation: The minimum window substring "BANC" includes 'A ...

ProblemGiven an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution, and you may not use the same element twice. You can return the answer in any order. Example 1: 1234Input: nums = [2,7,11,15], target = 9Output: [0,1]Explanation: Because nums[0] + nums[1] == 9, we return [0, 1]. Example 2: 123Input: nums = [3,2,4], target = 6Output: [1,2] Example 3: 123Input: nums = [3,3 ...

ProblemWrite an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number, and false if not. Example 1: 12345678Input: n = 19Output: ...

ProblemGiven a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: 1234Input: s = "leetcode", wordDict = ["leet","code"]Output: trueExplanation: Return true because "leetcode" can be segmented as "leet code". Example 2: 12345Input: s = "applepenap ...