There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai.
For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.
Return true if you can finish all courses. Otherwise, return false.
609. Find Duplicate File in System
Given a list paths of directory info, including the directory path, and all the files with contents in this directory, return all the duplicate files in the file system in terms of their paths. You may return the answer in any order.
A group of duplicate files consists of at least two files that have the same content.
A single directory info string in the input list has the following format:
- “root/d1/d2/…/dm f1.txt(f1_content) f2.txt(f2_content) … fn.txt(fn_content)”
It means there are n files (f1.txt, f2.txt … fn.txt) with content (f1_content, f2_content … fn_content) respectively in the directory “root/d1/d2/…/dm”. Note that n >= 1 and m >= 0. If m = 0, it means the directory is just the root directory.
The output is a list of groups of duplicate file paths. For each group, it contains all the file paths of the files that have the same content. A file path is a string that has the following format:
- “directory_path/file_name.txt”
341. Flatten Nested List Iterator
You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it.
Implement the NestedIterator class:
- NestedIterator(List
nestedList) Initializes the iterator with the nested list nestedList. - int next() Returns the next integer in the nested list.
- boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise.
244. Shortest Word Distance II
Design a data structure that will be initialized with a string array, and then it should answer queries of the shortest distance between two different strings from the array.
Implement the WordDistance class:
- WordDistance(String[] wordsDict) initializes the object with the strings array wordsDict.
- int shortest(String word1, String word2) returns the shortest distance between word1 and word2 in the array wordsDict.
You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Given a characters array tasks, representing the tasks a CPU needs to do, where each letter represents a different task. Tasks could be done in any order. Each task is done in one unit of time. For each unit of time, the CPU could complete either one task or just be idle.
However, there is a non-negative integer n that represents the cooldown period between two same tasks (the same letter in the array), that is that there must be at least n units of time between any two same tasks.
Return the least number of units of times that the CPU will take to finish all the given tasks.
There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai.
- For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.
Return the ordering of courses you should take to finish all courses. If there are many valid answers, return any of them. If it is impossible to finish all courses, return an empty array.
199. Binary Tree Right Side View
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.
The count-and-say sequence is a sequence of digit strings defined by the recursive formula:
- countAndSay(1) = “1”
- countAndSay(n) is the way you would “say” the digit string from countAndSay(n-1), which is then converted into a different digit string.
To determine how you “say” a digit string, split it into the minimal number of groups so that each group is a contiguous section all of the same character. Then for each group, say the number of characters, then say the character. To convert the saying into a digit string, replace the counts with a number and concatenate every saying.
For example, the saying and conversion for digit string “3322251”:
Given a positive integer n, return the nth term of the count-and-say sequence.
Given a string s which represents an expression, evaluate this expression and return its value.
The integer division should truncate toward zero.
Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval().
