1. strlen() returns the length of the string, exclude '\0'.

2. void swap(a, b) {a = a^b; b = a^b; a = a^b;} has bug in swap(a, a).

Is the size of given string just enough to store the final string?
Or the size is larger than what we need? 
(count the number of spaces first, then j = length + spaces * 2 - 1)

1. Use a picture to figure the rotating index.

2. Do NOT use special case as the example.

No need to check row[] and col[] separately.
for i -> for j -> if(row[i] || col[j]) {Mat[i][j] = 0;}

After remove a node, remember to deallocate this node space (use a temperary pointer).

Check with interviewers the given values in the questions.
(Will it execced ...? Will it be negative? ...)

Remember to move forward after assignment of a new node.

Reference: http://hawstein.com/posts/add-singly-linked-list.html

1. Member data and member function can NOT use the same name.

2. In class/struct, use -> for pointers, and use . for objects.

Remember the ; in the end of a class definition.

A classical example for recursive and OOP.

Reference: http://hawstein.com/posts/3.4.html

A example to learn inheritance.

Reference: https://github.com/xperzy/careerup150/blob/master/3-7.cpp

Need to how many nodes in each level.

1. The path does not cross a node.

2. Each node has a vector that contains all the values from its ancestors.

Reference: http://hawstein.com/posts/4.8.html

1. INT_MAX = ~(1 << 31), INT_MIN = (1 << 31)

2. Get sign-bit, if it is 1 (negative integer), other bis negate, then add 1.

In countone(int), while(n > 0) does NOT work for negative numbers to count the number of 1s.

n = n & (n-1) will clear the least significant bit in n.