[Draft] STD: Sort

This chapter describes the design and use of C ++ generic algorithm sort.

In my opinion, the generic Algorithm related to sorting is a relatively complex part of C ++.

The internal implementation of sort is not fixed. In different versions of C ++, the sort algorithms used may be different, however, the worst time complexity must be O (n log n ).

GNU Standard C ++ library adopts a three-step hybrid sorting method: First, it uses a province-specific sorting (itself uses a mixture of fast sorting and heap sorting), and then insert sorting.

See: http://en.wikipedia.org/wiki/Sort_ (C % 2B % 2b)

(For more information about province sorting, see: http://zh.wikipedia.org/wiki/%E5%86%85%E7%9C%81%E6%8E%92%E5%BA%8F)

It may be because the implementation method is not fixed, and the C ++ official website does not provide relevant implementation methods.

Let's take a look at the sort description on the C ++ official website.

Http://www.cplusplus.com/reference/algorithm/sort/

(Note: The following content is my understanding of the content on the C ++ official website. If it is not accurate, please forgive me)

• Sort function declaration:

The sort function has two forms,

One is the comparison using operator by default:

template <class RandomAccessIterator>void sort (RandomAccessIterator first, RandomAccessIterator last);

One is the form of custom comparison:

template <class RandomAccessIterator, class Compare>void sort (RandomAccessIterator first, RandomAccessIterator last, Compare comp);

Therefore, if you want to sort a set of data of the custom type, you have two options: 1. Reload operator <; 2. Use the second form.

• The role of the sort function:

Sort the elements in the [first, last) sequence (if the first method above is used, the elements are sorted in descending order ).

Non-stable sorting, that is, equal two elements, cannot guarantee their original order after sorting. (If you need stable sorting, use stable_sort ).

Other content (not detailed enough ):

• Time Complexity of the sort function:

Worst time complexity O (n log n)

• Sorting method of the sort function:

Non-stable sorting (use stable_sort if stable sorting is required ).

In different versions of C ++, the Sorting Algorithm Used by sort may be different. GNU adopts a mix of provincial sorting and insert sorting.

The following is a simple example.

#include <algorithm>#include <iostream>#include <vector>using std::cout;using std::endl;using std::vector;class Whatever{public:    Whatever(int size, char name)        : mSize(size), mName(name)    {}    int getSize() { return mSize; }    char getName() { return mName; }    bool operator< (const Whatever& what) const    {        return (this->mSize < what.mSize);    }private:    int mSize;    char mName;};void print(vector<int> vec){    for (vector<int>::iterator iter = vec.begin(); iter != vec.end(); iter++)    {        cout << *iter << ‘ ‘;    }    cout << endl;}void print(vector<Whatever> vec){    for (vector<Whatever>::iterator iter = vec.begin(); iter != vec.end(); iter++)    {        cout << iter->getSize() << iter->getName() << ‘ ‘;    }    cout << endl;}bool compare(int i, int j){    return (i > j);}bool compareWhat(Whatever i, Whatever j){    return (i < j);}int main(void){    int vecVal[] = {12, 10, 13, 15, 20, 18, 11};    vector<int> vec(vecVal, vecVal+7);    sort(vec.begin(), vec.end());    print(vec);    sort(vec.begin(), vec.end(), compare);    print(vec);    vector<Whatever> vecWhat;    for (int i = 0; i < 100; i++)    {        Whatever what(rand()%50, char(97+rand()%25));        vecWhat.push_back(what);    }    print(vecWhat);    sort(vecWhat.begin(), vecWhat.end(), compareWhat);    print(vecWhat);    return 0;}

 

[Draft] STD: Sort