good practice

http://www.tutorialspoint.com/developers_best_practices/developers_best_practices_discussion.htm

Web

OSI, TCP/IP

These three pages are so far the best to simply understand OSI, TCP/IP.

http://www.hardwaresecrets.com/the-osi-reference-model-for-network-protocols/

http://www.hardwaresecrets.com/how-tcp-ip-protocol-works-part-1/

http://www.hardwaresecrets.com/how-tcp-ip-protocol-works-part-2/

What really happens when you navigate to a URL

HTML tutorial

http://www.tutorialspoint.com/html/html_overview.htm

goood solutions for tree traversal

TracyJanuary 26, 2011 at 7:20 pm

@1337c0d3r:
I'm quite sure that my code of using one stack for post-order traversal works. You can use the same example above to go through it. I made iterative in-order, pre-order and post-order traversal as similar as possible:

void postorderNoR(const Node *root)
{
stack s;
const Node *itr = root;

while (itr || !s.empty()) {
if (!itr) {
while (!s.empty() &&
itr == s.top()->right) {
itr = s.top();
s.pop();
printf("%d ",itr->value);
}
itr = s.empty() ? NULL : s.top()->right;
}
else
{
s.push(itr);
itr = itr->left;
}
}
}

// *********************

void inorderNoR(const Node *root)
{
stack s;
const Node *itr = root;

while (itr || !s.empty()){
if (!itr){
itr = s.top();
s.pop();
printf("%d ",itr->value);
itr = itr->right;
}
else{
s.push(itr);
itr = itr->left;
}
}
}

// *********************

void preorderNoR(const Node *root)
{
stack s;
const Node *itr = root;

while (itr || !s.empty()){
if (!itr){
itr = s.top();
s.pop();
itr = itr->right;
}
else{
printf("%d ",itr->value);
s.push(itr);
itr = itr->left;
}
}
}

0

Pay Attention!!

Graph

directed graph or undirected graph?
The methods of graph traversal?
http://articles.leetcode.com/2012/05/clone-graph-part-i.html

Number
always consider if the algorithm will over flow!!!!!!
if negative or zero number will impact the final result!!!!!!
http://articles.leetcode.com/2012/01/palindrome-number.html

String
'a' to 'z'? Digits? Upper case letter? Does it contain ASCII characters only? Or even unicode character sets?
http://articles.leetcode.com/2011/05/longest-substring-without-repeating-characters.html

Tree
duplications? 
http://articles.leetcode.com/2011/04/construct-binary-tree-from-inorder-and-preorder-postorder-traversal.html

Longest Palindromic Substring

Longest Palindromic Substring

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

--------------------- thinking -----------------------------

https://leetcode.com/discuss/32204/simple-c-solution-8ms-13-lines
http://articles.leetcode.com/2011/11/longest-palindromic-substring-part-i.html
http://articles.leetcode.com/2011/11/longest-palindromic-substring-part-ii.html
http://www.felix021.com/blog/read.php?2040

word ladder

Word Ladder

 Given two words (beginWord and endWord), and a dictionary, find the length of shortest transformation sequence from beginWord to endWord, such that:

1. Only one letter can be changed at a time
2. Each intermediate word must exist in the dictionary

For example,

Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]

As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

Note:

• Return 0 if there is no such transformation sequence.
• All words have the same length.
• All words contain only lowercase alphabetic characters.

--------------- thinking -----------------------
A lot of optimizations are discussed in this post!!!! And why my codes is memory limit exceed!!!
http://www.cnblogs.com/linyx/p/3706688.html

Detect Cycle in a Directed Graph

Detect Cycle in a Directed Graph

Given a directed graph, check whether the graph contains a cycle or not. Your function should return true if the given graph contains at least one cycle, else return false. For example, the following graph contains three cycles 0->2->0, 0->1->2->0 and 3->3, so your function must return true.
Solution
Depth First Traversal can be used to detect cycle in a Graph. DFS for a connected graph produces a tree. There is a cycle in a graph only if there is a back edge present in the graph. A back edge is an edge that is from a node to itself (selfloop) or one of its ancestor in the tree produced by DFS. In the following graph, there are 3 back edges, marked with cross sign. We can observe that these 3 back edges indicate 3 cycles present in the graph.

For a disconnected graph, we get the DFS forrest as output. To detect cycle, we can check for cycle in individual trees by checking back edges.

----------------------- thinking ----------------------------------