题目描述: 班上有 N 名学生.其中有些人是朋友,有些则不是.他们的友谊具有是传递性.如果已知 A 是 B 的朋友,B 是 C 的朋友,那么我们可以认为 A 也是 C 的朋友.所谓的朋友圈,是指所有朋友的集合. 给定一个 N * N 的矩阵 M,表示班级中学生之间的朋友关系.如果M[i][j] = 1,表示已知第 i 个和 j 个学生互为朋友关系,否则为不知道.你必须输出所有学生中的已知的朋友圈总数. 示例 1: 输入: [[1,1,0], [1,1,0], [0,0,1]] 输出: 2 说明:

# 增强学习成果 有一个研究成果,在学习中传授他人知识和讨论是最高效的做法,而看书则是最低效的做法(具体研究成果没找到地址).我写LeetCode博客主要目的是增强学习成果.当然,我也想出名,然而不知道能否出名. # 给算法的新手们提供一种思考方式的参考 提前说明,本人也不是高手. 算法这个东西有点玄乎.很多新手(包括我)初期入门的时候都学的是<算法导论>,然而我并不觉得<算法导论>是一本学习算法很好的书. 我们设计算法的流程,并不是像<算法导论>那样,好像天生就知道这

终于将LeetCode的免费题刷完了,真是漫长的第一遍啊,估计很多题都忘的差不多了,这次开个题目汇总贴,并附上每道题目的解题连接,方便之后查阅吧~ 477 Total Hamming Distance 44.10% Meidum 475 Heaters  30.20% Easy 474 Ones and Zeroes  34.90% Meidum 473 Matchsticks to Square  31.80% Medium 472 Concatenated Words 29.20% Hard

Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than k times. Example 1: Input: s = "aaabb", k = 3 Output: 3 The longest substring is "aaa"

题目链接:Path Sum II | LeetCode OJ Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ / \ 7 2 5 1 return [ [5,4,11,2],

题目链接:Path Sum | LeetCode OJ Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11

题目链接:Balanced Binary Tree | LeetCode OJ Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more tha

题目链接:Same Tree | LeetCode OJ Given two binary trees, write a function to check if they are equal or not. Two binary trees are considered equal if they are structurally identical and the nodes have the same value. Tags: Depth-first Search 分析 很基本的一道深度优

题目链接:Recover Binary Search Tree | LeetCode OJ Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. Note: A solution using O(n) space is pretty straight forward. Could you devise a constan

题目链接:Validate Binary Search Tree | LeetCode OJ Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right

题目链接:Symmetric Tree | LeetCode OJ Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the following is not: 1 / \ 2 2 \ \ 3 3 Note: B

题目链接:Sudoku Solver | LeetCode OJ Write a program to solve a Sudoku puzzle by filling the empty cells. Empty cells are indicated by the character '.'. You may assume that there will be only one unique solution. A sudoku puzzle... ...and its solution n

题目链接:Valid Sudoku | LeetCode OJ Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. The Sudoku board could be partially filled, where empty cells are filled with the character '.'. A partially filled sudoku which is valid. Note:

题目链接:Populating Next Right Pointers in Each Node II | LeetCode OJ Follow up for problem "Populating Next Right Pointers in Each Node". What if the given tree could be any binary tree? Would your previous solution still work? Note: You may only u

题目链接:Populating Next Right Pointers in Each Node | LeetCode OJ Given a binary tree struct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next; } Populate each next pointer to point to its next right node. If there is no next ri

最近刷LeetCode比较频繁,就购买了官方的参考电子书 (CleanCodeHandbook),里面有题目的解析和范例源代码,可以省去非常多寻找免费经验分享内容和整理这些资料的时间.惊喜的是,里面的所有源代码都是用java语言写的. 接下来的一段时间里,我会将里面的大部分内容翻译成中文,再加上一些小y自己的解法和扩展内容,以博客的形式发在博客园.我想,这会是一件非常有趣的事情. 以下是翻译的前言部分,第1.4题以及其解析部分. 前言: 嗨,各位刷LeetCode的小伙伴们. 就像你们看到这本书

2015年即将过去,最近在回顾和总结过去一年的工作经历,发现自己并不能算是一名合格的程序员. Google某前员工Lucida在文章<白板编程访谈——Why,What,How>当中写道: 程序员可以被分为两种: 先确认前条件/不变式/终止条件/边界条件,然后写出正确的代码 先编写代码,然后通过各种用例/测试/调试对程序进行调整,最后得到似乎正确的代码 我个人保守估计前者开发效率至少是后者的10倍,因为前者不需要浪费大量时间在编码-调试-编码这个极其耗时的循环上. 很不幸的是,我觉得自己应该被归

Sept. 22, 2015 学一道算法题, 经常回顾一下. 第二次重温, 决定增加一些图片, 帮助自己记忆. 在网上找他人的资料, 不如自己动手. 把从底向上树的算法搞通俗一些. 先做一个例子: 9/22/2015 Go over one example to build some muscle memory about this bottom up, O(1) solution to find the root node in subtree function. Sorted List: 1

Sept. 13, 2015 Spent more than a few hours to work on the leetcode problem, and my favorite blogs about this problems: 1. http://siddontang.gitbooks.io/leetcode-solution/content/tree/construct_binary_tree.html 2.http://blog.csdn.net/linhuanmars/artic

The Hamming distance between two integers is the number of positions at which the corresponding bits are different. Now your job is to find the total Hamming distance between all pairs of the given numbers. Example: Input: 4, 14, 2 Output: 6 Explanat

Winter is coming! Your first job during the contest is to design a standard heater with fixed warm radius to warm all the houses. Now, you are given positions of houses and heaters on a horizontal line, find out minimum radius of heaters so that all