Chapter 4
Some people find the “90/10” rule helpful: 90 percent of the running time of most programs is spent in only
10 percent of the code (Hennessy and Patterson, 2002)

Use a vector instead of an array whenever possible.
Vectors provide fast (constant time) element insertion and deletion at the end of the vector, but slow
(linear time) insertion and deletion anywhere else. Insertion and deletion are slow because the operation
must move all the elements “down” or “up” by one to make room for the new element or to fill the
space left by the deleted element. Like arrays, vectors provide fast (constant time) access to any of their
elements.
You should use a vector in your programs when you need fast access to the elements, but do not plan to
add or remove elements often. A good rule of thumb is to use a vector whenever you would have used
an array.

The name deque is an abbreviation for a double-ended queue. A deque is partway between a vector and a
list, but closer to a vector. Like a vector, it provides quick (constant time) element access. Like a list, it
provides fast (amortized constant time) insertion and deletion at both ends of the sequence. However,
unlike a list, it provides slow (linear time) insertion and deletion in the middle of the sequence.
You should use a deque instead of a vector when you need to insert or remove elements from either end
of the sequence but still need fast access time to all elements. However, this requirement does not apply
to many programming problems; in most cases a vector or queue should suffice.

A set in STL is a collection of elements. Although the mathematical definition of a set implies an
unordered collection, the STL set stores the elements in an ordered fashion so that it can provide reasonably
fast lookup, insertion, and deletion.
Use a set instead of a vector or list if you want equal performance for insertion, deletion,and lookup.
Note that a set does not allow duplication of elements. That is, each element in the set must be unique. If
you want to store duplicate elements, you must use a multiset.

Chapter8
Initializer lists allow initialization of data members at the time of their creation.
An initializer list allows you to provide initial values for data members as they are created, which is more efficient than assigning values to them later.
However, several data types must be initialized in an initializer list. The following table summarizes them:a、 const data members； b、Reference data members C、Object data members or Superclasses without default constructors
Initializer lists initialize data members in their declared order in the class definition,not their order in the list.

Chapter9
Pass objects by const reference instead of by value.
The default semantics for passing arguments to functions in C++ is pass-by-value. That means that the function or method receives a copy of the variable, not the variable itself. Thus, whenever you pass an object to a function or method the compiler calls the copy constructor of the new object to initialize it. The copy constructor is also called whenever you return an object from a function or method.