id18. 4Sum Add to List QuestionEditorial Solution My Submissions
Total Accepted: 101633
Total Submissions: 394751
Difficulty: Medium
Contributors: Admin
Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note: The solution set must not contain duplicate quadruplets.

For example, given array S = [1, 0, -1, 0, -2, 2], and target = 0.

A solution set is:
[
[-1, 0, 0, 1],
[-2, -1, 1, 2],
[-2, 0, 0, 2]
]

学习了一段QTwidgets编程，自己设计了cortfly-一款基于局域网得使用工具。
update v1.0

1. 软件采用互联网TCP/UDP协议设计，支持数据包重传保证文件传输的稳定性。
2. 局域网聊天
3. 文件对传
4. 实验室论坛一键连接
5. 实验室服务器登陆

软件下载：www.cortfly.com
github源码： https://github.com/unsky/cortfly

Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string “23”
Output: [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”].

1. 3Sum Closest Add to List QuestionEditorial Solution My Submissions
   Total Accepted: 109596
   Total Submissions: 358454
   Difficulty: Medium
   Contributors: Admin
   Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

   For example, given array S = {-1 2 1 -4}, and target = 1.

   The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

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QFramae 类是带有边框得基类，它得子类有最常用得标签部件QLabel,QLCDNumber,QSplitter,QStackedWidget,QToolBox,QAbstractScrollArea类，其中再QT中凡是带有Abstract字样得类都是抽象基类，对于抽象基类我们不能直接使用，但是可以继承该类实现自己得类。或者使用他提供得子类，

Deep Learning Strong Parts for Pedestrian Detection 是发表在iccv2015的文章。

Qt提供了丰富的标准对话框，全部继承自QDialog类，并且加入了自己的特色。

信号和槽的机制简单理解就是，做一件事，发射一种信号，然后执行槽内的程序。

对话框按照是否可以在运行时可以和其他窗口进行交互可以分为：模态与非模态对话框。

Id.15. 3Sum Add to List QuestionEditorial Solution My Submissions
Total Accepted: 165869
Total Submissions: 802806
Difficulty: Medium
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Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.