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Write an algorithm to determine if a number 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, and 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 numbers. Example:  19 is a happy number 1 2  + 9 2  = 82 8 2  + 2 2  = 68 6 2  + 8 2  = 100 1 2  + 0 2  + 0 2  = 1 Ref:  https://leetcode.com/problems/happy-number/

Given a string, find the length of the  longest substring  without repeating characters. Examples: Given  "abcabcbb" , the answer is  "abc" , which the length is 3. Given  "bbbbb" , the answer is  "b" , with the length of 1. Given  "pwwkew" , the answer is  "wke" , with the length of 3. Note that the answer must be a  substring ,  "pwke"  is a  subsequence  and not a substring. Ref:  https://leetcode.com/problems/longest-substring-without-repeating-characters/

今天在研究如何使用Java Mail的API從GMail寄信出去，以及使用EWS API從Exchange寄信，寫了一些測試用的Code分享給大家。 一、用JavaMail從GMail寄信 因為GMail講求安全性，所以在Java Mail的設定上會比較複雜， SMTP 伺服器的通訊埠設為 465 (適用 SSL/TLS) 和 587 (適用 STARTTLS)，而在這個例子，我們使用STARTTLS，這個協定就是為了加密從用戶端到伺服器端的連線，會對EMAIL在寄送時更加安全。另外，GMail也有開啟SMTP AUTH的功能，所以我們要得到使用者的帳號密碼才可以寄送。 而如果你有開兩步驟，需要另外建立一個「應用程式密碼」；沒有開兩步驟，則是需要開起「允許安全性較低的應用程式」才能夠正確執行，要不然會報錯。 部份程式碼： 完整程式碼： https://github.com/jimc1682000/JavaMailLab/blob/master/src/tw/com/jimmy/lab/SendFromGMailUsingJavaMailLab.java Ref: http://pclevin.blogspot.tw/2014/11/java-mail-gmail-smtp-server.html https://support.google.com/mail/answer/78775?hl=zh-Hant

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list. Input:  (2 -> 4 -> 3) + (5 -> 6 -> 4) Output:  7 -> 0 -> 8 /**  * Definition for singly-linked list.  * public class ListNode {  *     int val;  *     ListNode next;  *     ListNode(int x) { val = x; }  * }  */ Ref:  https://leetcode.com/problems/add-two-numbers/

Given an array of integers, return  indices  of the two numbers such that they add up to a specific target. You may assume that each input would have  exactly  one solution. Example: Given nums = [2, 7, 11, 15], target = 9, Because nums[ 0 ] + nums[ 1 ] = 2 + 7 = 9, return [ 0 , 1 ]. UPDATE (2016/2/13): The return format had been changed to  zero-based  indices. Please read the above updated description carefully. Ref:  https://leetcode.com/problems/two-sum/

Related to question  Excel Sheet Column Title Given a column title as appear in an Excel sheet, return its corresponding column number. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 Ref:  https://leetcode.com/problems/excel-sheet-column-number/

Given a positive integer, return its corresponding column title as appear in an Excel sheet. For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27 -> AA 28 -> AB Ref: https://leetcode.com/problems/excel-sheet-column-title/

The demons had captured the princess ( P ) and imprisoned her in the bottom-right corner of a dungeon. The dungeon consists of M x N rooms laid out in a 2D grid. Our valiant knight ( K ) was initially positioned in the top-left room and must fight his way through the dungeon to rescue the princess. The knight has an initial health point represented by a positive integer. If at any point his health point drops to 0 or below, he dies immediately. Some of the rooms are guarded by demons, so the knight loses health ( negative  integers) upon entering these rooms; other rooms are either empty ( 0's ) or contain magic orbs that increase the knight's health ( positive  integers). In order to reach the princess as quickly as possible, the knight decides to move only rightward or downward in each step.

最近發現了一個不錯的網站，叫做 LeetCode ，這個網站裡面有著大量的題目，大部份都是在面試程式設計時常常被問到的問題，很適合想要找工作的人來練練手，又或是覺得自己的技術底不夠，想要再加強的人，來練習一下。 他內建了線上執行CODE和判斷程式是否執行錯誤/逾時的功能，所以有些時候，就算你的演算法都是正確的，但只要逾時，那麼還是不算通過，所以這個時候就可以研究一下其他人是怎麼寫的，他內建有論壇功能，而你也可以使用題目下去搜尋，基本上都可以找到許多參考資料。 也許有的人會覺得這種題庫的東西很沒有意義，而且很多答案也都可以上網找到，那更沒有練習的必要，但我認為，至少對我而言，有些解法我一開始是沒辦法直覺想到，需要另外花時間才能夠思考得到，在現在分秒必爭的大環境下，如果我能夠直覺想到一些解法，我相信一定有著很大的加分，更何況有些解法是我想都沒有想過的呢？ 之後我會於週一到週五每天更新一篇LeetCode解法的文章，作為一個紀錄，而大家如果有什麼問題，也都可以隨時討論，雖然我不見得能夠直接回答，但至少我也會找出一些相關資料再提供大家討論。 那麼，就開始CODING吧！