Articles
-
445 - Add Two Numbers II
You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself.
-
415 - Add Strings
Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.
-
228 - Summary Ranges
Given a sorted integer array without duplicates, return the summary of its ranges. For example, given [0,1,2,4,5,7], return [“0->2”,”4->5”,”7”].
-
236 - Lowest Common Ancestor of a Binary Tree
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).
-
572 - Subtree of Another Tree
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. The tree s could also be considered as a subtree of itself.
-
339 - Nested List Weight Sum
Given a nested list of integers, return the sum of all integers in the list weighted by their depth. Each element is either an integer, or a list – whose elements may also be integers or other lists.
-
364 - Nested List Weight Sum II
Given a nested list of integers, return the sum of all integers in the list weighted by their depth. Each element is either an integer, or a list – whose elements may also be integers or other lists. Different from the previous question where weight is increasing from root to leaf, now the weight is defined from bottom up. i.e., the leaf level integers have weight 1, and the root level integers have the largest weight.
-
348 - Design Tic Tac Toe
Design a Tic-tac-toe game that is played between two players on a n x n grid. You may assume the following rules:
-
44 - Wildcard Matching
Implement wildcard pattern matching with support for ‘?’ and ‘*’.
-
72 - Edit Distance
Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.) You have the following 3 operations permitted on a word: Insert a character, Delete a character, Replace a character.
-
239 - Sliding Window Maximum
Given an array of n integer with duplicate number, and a moving window(size k), move the window at each iteration from the start of the array, find the maximum number inside the window at each moving
-
412 - Fizz Buzz
Given number n. Print number from 1 to n. But: when number is divided by 3, print “fizz”, when number is divided by 5, print “buzz”, when number is divided by both 3 and 5, print “fizz buzz”.
-
140 - Word Break II
Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences.
-
811 - Subdomain Visit Count
A website domain like “discuss.leetcode.com” consists of various subdomains. At the top level, we have “com”, at the next level, we have “leetcode.com”, and at the lowest level, “discuss.leetcode.com”. When we visit a domain like “discuss.leetcode.com”, we will also visit the parent domains “leetcode.com” and “com” implicitly. Now, call a “count-paired domain” to be a count (representing the number of visits this domain received), followed by a space, followed by the address. An example of a count-paired domain might be “9001 discuss.leetcode.com”. We are given a list cpdomains of count-paired domains. We would like a list of count-paired domains, (in the same format as the input, and in any order), that explicitly counts the number of visits to each subdomain.
-
780 - Reaching Points
A move consists of taking a point (x, y) and transforming it to either (x, x+y) or (x+y, y). Given a starting point (sx, sy) and a target point (tx, ty), return True if and only if a sequence of moves exists to transform the point (sx, sy) to (tx, ty). Otherwise, return False.**
-
362 - Design Hit Counter
Design a hit counter which counts the number of hits received in the past 5 minutes (i.e., the past 300 seconds).
-
341 - Flatten Nested List Iterator
Given a nested list of integers, implement an iterator to flatten it. Each element is either an integer, or a list – whose elements may also be integers or other lists.
-
227 - Basic Calculator II
Given a string s which represents an expression, evaluate this expression and return its value.
-
45 - Jump Game II
Given an array of non-negative integers, you are initially positioned at the first index of the array. Each element in the array represents your maximum jump length at that position. Your goal is to reach the last index in the minimum number of jumps.
-
1048 - Longest String Chain
Given a list of words, each word consists of English lowercase letters. Let’s say word1 is a predecessor of word2 if and only if we can add exactly one letter anywhere in word1 to make it equal to word2. For example, “abc” is a predecessor of “abac”. A word chain is a sequence of words [word_1, word_2, …, word_k] with k >= 1, where word_1 is a predecessor of word_2, word_2 is a predecessor of word_3, and so on. Return the longest possible length of a word chain with words chosen from the given list of words.
-
430 - Flatten A Multilevel Doubly Linked List
You are given a doubly linked list which in addition to the next and previous pointers, it could have a child pointer, which may or may not point to a separate doubly linked list. These child lists may have one or more children of their own, and so on, to produce a multilevel data structure, as shown in the example below. Flatten the list so that all the nodes appear in a single-level, doubly linked list. You are given the head of the first level of the list.
-
621 - Task Scheduler
Given a char array representing tasks CPU need to do. It contains capital letters A to Z where different letters represent different tasks. Tasks could be done without original order. Each task could be done in one interval. For each interval, CPU could finish one task or just be idle. However, there is a non-negative cooling interval n that means between two same tasks, there must be at least n intervals that CPU are doing different tasks or just be idle. You need to return the least number of intervals the CPU will take to finish all the given tasks.
-
759 - Employee Free Time
We are given a list schedule of employees, which represents the working time for each employee. Each employee has a list of non-overlapping Intervals, and these intervals are in sorted order. Return the list of finite intervals representing common, positive-length free time for all employees, also in sorted order.
-
460 - Lfu Cache
Design and implement a data structure for Least Frequently Used (LFU) cache. It should support the following operations: get and put.**
-
547 - Friend Circles
There are N students in a class. Some of them are friends, while some are not. Their friendship is transitive in nature. For example, if A is a direct friend of B, and B is a direct friend of C, then A is an indirect friend of C. And we defined a friend circle is a group of students who are direct or indirect friends. Given a N*N matrix M representing the friend relationship between students in the class. If M[i][j] = 1, then the ith and jth students are direct friends with each other, otherwise not. And you have to output the total number of friend circles among all the students.
-
1181 - Before And After Puzzle
Given a list of phrases, generate a list of Before and After puzzles. A phrase is a string that consists of lowercase English letters and spaces only. No space appears in the start or the end of a phrase. There are no consecutive spaces in a phrase. Before and After puzzles are phrases that are formed by merging two phrases where the last word of the first phrase is the same as the first word of the second phrase. Return the Before and After puzzles that can be formed by every two phrases phrases[i] and phrases[j] where i != j. Note that the order of matching two phrases matters, we want to consider both orders. You should return a list of distinct strings sorted lexicographically.
-
735 - Asteroid Collision
We are given an array asteroids of integers representing asteroids in a row. For each asteroid, the absolute value represents its size, and the sign represents its direction (positive meaning right, negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet, the smaller one will explode. If both are the same size, both will explode. Two asteroids moving in the same direction will never meet.
-
981 - Time Based Key Value Store
```python from collections import defaultdict class TimeMap:
-
642 - Design Search Autocomplete System
Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character ‘#’). For each character they type except ‘#’, you need to return the top 3 historical hot sentences that have prefix the same as the part of sentence already typed. Here are the specific rules:
-
336 - Palindrome Pairs
Given a list of unique words, find all pairs of distinct indices (i, j) in the given list, so that the concatenation of the two words, i.e. words[i] + words[j] is a palindrome.
