原文链接: https://leetcode-cn.com/problems/guess-number-higher-or-lower-ii 英文原文We are playing the Guessing Game. The game will work as follows: I pick a number between 1 and n. You guess a number. If you guess the right number, you win the game. If you g…

原文链接: https://leetcode-cn.com/problems/wiggle-subsequence 英文原文A wiggle sequence is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positi…

原文链接: https://leetcode-cn.com/problems/combination-sum-iv 英文原文Given an array of distinct integers nums and a target integer target, return the number of possible combinations that add up to target. The answer is guaranteed to fit in a 32-bit integer.…

原文链接: https://leetcode-cn.com/problems/kth-smallest-element-in-a-sorted-matrix 英文原文Given an n x n matrix where each of the rows and columns is sorted in ascending order, return the kth smallest element in the matrix. Note that it is the kth smallest …

原文链接: https://leetcode-cn.com/problems/insert-delete-getrandom-o1 英文原文Implement 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 i…

原文链接: https://leetcode-cn.com/problems/insert-delete-getrandom-o1-duplicates-allowed 英文原文RandomizedCollection is a data structure that contains a collection of numbers, possibly duplicates (i.e., a multiset). It should support inserting and removing …

原文链接: https://leetcode-cn.com/problems/linked-list-random-node 英文原文Given a singly linked list, return a random node's value from the linked list. Each node must have the same probability of being chosen. Implement the Solution class: Solution(ListNod…

原文链接: https://leetcode-cn.com/problems/ransom-note 英文原文Given two stings ransomNote and magazine, return true if ransomNote can be constructed from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: I…

原文链接: https://leetcode-cn.com/problems/shuffle-an-array 英文原文Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling. Implement the Solution cl…

原文链接: https://leetcode-cn.com/problems/mini-parser 英文原文Given a string s represents the serialization of a nested list, implement a parser to deserialize it and return the deserialized NestedInteger. Each element is either an integer or a list whose e…

原文链接: https://leetcode-cn.com/problems/lexicographical-numbers 英文原文Given an integer n, return all the numbers in the range [1, n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space. Example 1…

原文链接: https://leetcode-cn.com/problems/first-unique-character-in-a-string 英文原文Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1. Example 1: Input: s = "leetcode" Output: 0 Example 2: …

原文链接: https://leetcode-cn.com/problems/longest-absolute-file-path 英文原文Suppose we have a file system that stores both files and directories. An example of one system is represented in the following picture: Here, we have dir as the only directory in t…

原文链接: https://leetcode-cn.com/problems/find-the-difference 英文原文You are given two strings s and t. String t is generated by random shuffling string s and then add one more letter at a random position. Return the letter that was added to t. Example 1: …

原文链接: https://leetcode-cn.com/problems/perfect-rectangle 英文原文Given an array rectangles where rectangles[i] = [xi, yi, ai, bi] represents an axis-aligned rectangle. The bottom-left point of the rectangle is (xi, yi) and the top-right point of it is (a…

原文链接: https://leetcode-cn.com/problems/is-subsequence 英文原文Given two strings s and t, return true if s is a subsequence of t, or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can b…

原文链接: https://leetcode-cn.com/problems/utf-8-validation 英文原文Given an integer array data representing the data, return whether it is a valid UTF-8 encoding. A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules: For a 1-b…

原文链接: https://leetcode-cn.com/problems/decode-string 英文原文Given an encoded string, return its decoded string. The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. Note that k i…

原文链接: https://leetcode-cn.com/problems/longest-substring-with-at-least-k-repeating-characters 英文原文Given a string s and an integer k, return the length of the longest substring of s such that the frequency of each character in this substring is greate…

原文链接: https://leetcode-cn.com/problems/rotate-function 英文原文You are given an integer array nums of length n. Assume arrk to be an array obtained by rotating nums by k positions clock-wise. We define the rotation function F on nums as follow: F(k) = 0 …

原文链接: https://leetcode-cn.com/problems/integer-replacement 英文原文Given a positive integer n, you can apply one of the following operations: If n is even, replace n with n / 2. If n is odd, replace n with either n + 1 or n - 1. Return the minimum number…

原文链接: https://leetcode-cn.com/problems/random-pick-index 英文原文Given an integer array nums with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array. Implement the …

原文链接: https://leetcode-cn.com/problems/nth-digit 英文原文Given an integer n, return the nth digit of the infinite integer sequence [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, ...]. Example 1: Input: n = 3 Output: 3 Example 2: Input: n = 11 Output: 0 Explanation:…

原文链接: https://leetcode-cn.com/problems/evaluate-division 英文原文You are given an array of variable pairs equations and an array of real numbers values, where equations[i] = [Ai, Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi…

原文链接: https://leetcode-cn.com/problems/remove-k-digits 英文原文Given string num representing a non-negative integer num, and an integer k, return the smallest possible integer after removing k digits from num. Example 1: Input: num = "1432219", k = 3 Out…

原文链接: https://leetcode-cn.com/problems/frog-jump 英文原文A frog is crossing a river. The river is divided into some number of units, and at each unit, there may or may not exist a stone. The frog can jump on a stone, but it must not jump into the water. …

原文链接: https://leetcode-cn.com/problems/convert-a-number-to-hexadecimal 英文原文Given an integer num, return a string representing its hexadecimal representation. For negative integers, two’s complement method is used. All the letters in the answer …

原文链接: https://leetcode-cn.com/problems/sum-of-left-leaves 英文原文Given the root of a binary tree, return the sum of all left leaves. Example 1: Input: root = [3,9,20,null,null,15,7] Output: 24 Explanation: There are two left leaves in the binary tree, w…

原文链接: https://leetcode-cn.com/problems/queue-reconstruction-by-height 英文原文You are given an array of people, people, which are the attributes of some people in a queue (not necessarily in order). Each people[i] = [hi, ki] represents the ith person of …

原文链接: https://leetcode-cn.com/problems/trapping-rain-water-ii 英文原文Given an m x n integer matrix heightMap representing the height of each unit cell in a 2D elevation map, return the volume of water it can trap after raining. Example 1: Input: heightM…