netstat显示的连接状态有几种WAIT: FIN_WAIT_1,FIN_WAIT_2,CLOSE_WAIT和TIME_WAIT. 他们的含义要从TCP的连接中断过程说起

traceroute 有使用两种：使用ICMP的和使用UDP的。Microsoft使用ICMP，所以win95上发出的traceRT应使用的是ICMP，但我没有用 sniffer查过；其它包括unix和cisco router都使用UDP.

Given 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.

For example:
Given the following binary tree,

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

You should return [1, 3, 4].

Credits:
Special thanks to @amrsaqr for adding this problem and creating all test cases.

Single Number I, all twice except one single

Single Number II All numbers occurs triple times except one once

Single Number II All numbers occurs triple times except one twice

Single Number III  all twice numbers, except two single Number