插入排序：我做错了什么？

Question

我正在尝试进行插入排序。这首歌是一个简单的结构，包含艺术家和标题属性。如果第一首歌曲的歌名在第二首歌曲的歌名之前，我将 CompareTitle(Song& s1, Song& s2) 称为 returns true。当代码的交换部分被注释掉时，排序条件似乎工作正常。如果没有，我会收到此错误。我不确定如何处理它：

playlist.cc:192:22: error: object of type 'Song' cannot be assigned because its copy assignment operator is implicitly deleted *itr = j;

//do insertion sort
for(auto itr = newSongList.begin(); itr != newSongList.end(); ++itr)
{

    for(auto jtr=itr; jtr != newSongList.begin(); --jtr){
        cout << itr->GetTitle() << " " << jtr->GetTitle() << endl;
        // if s1 is not before s2 then swap them
        if(!Song::CompareTitle(*itr, *jtr)){
            cout << "Swap True (" << itr->GetTitle() << "," << jtr->GetTitle() << " )"<< endl;
            Song i = Song(itr->GetTitle(),itr->GetArtist());
            Song j = Song(jtr->GetTitle(), jtr->GetArtist());

            *itr = j;
            *jtr = i;

            cout << "Swap After (" << jtr->GetTitle() << "," << itr->GetTitle() << endl;
        }
    }
}

以下是歌曲和播放列表的结构：

#ifndef PLAYLIST_H
#define PLAYLIST_H

#include <functional>   // For std::function
#include <string>
#include <list>

using namespace std;

extern void SongCallback();

class Song {
  public:
    explicit Song(const string& title, const string& artist,
        const function<void()> = &SongCallback);
        const string& GetTitle() const;
        const string& GetArtist() const;
        bool operator==(const Song& s) const;
        bool operator()(const Song& s) const;

        static bool CompareTitle(const Song& s1, const Song& s2);
        static bool CompareArtistTitle(const Song& s1, const Song& s2);

private:
    const string title_;
    const string artist_;
    const function<void()> callback_;
};

class Playlist {
public:
    explicit Playlist() {}
    void AddSong(const string& title, const string& artist);
    unsigned int RemoveSongs(const string& title, const string& artist);
    list<Song> PlaylistSortedByTitle() const;
    list<Song> PlaylistSortedByArtistTitle() const;
    unsigned int NumSongs() const;
    unsigned int NumSongs(const string& artist) const;

private:
    list<Song> songs_;
};

#endif // PLAYLIST_H

Answer 1

似乎每次您应该交换两个元素的迭代器时，您实际上是在 itr 和 jtr 之前将元素添加到容器中。

for(auto itr = newSongList.begin(); itr != newSongList.end(); ++itr)
{

    for(auto jtr=itr; jtr != newSongList.begin(); --jtr){
        cout << itr->GetTitle() << " " << jtr->GetTitle() << endl;
        // if s1 is not before s2 then swap them
        if(!Song::CompareTitle(*itr, *jtr)){
            swap(*itr, *jtr);
        }
    }
}

在这里您可以使用 std::swap 作为交换功能，或者编写您自己的函数来切换歌曲的标题和艺术家，以及可能添加到其中的任何其他成员。 std::iter_swap 也可以作为替代。

std::swap on CPP reference

std::iter_swap on CPP reference

Answer 2

因为你有 const title_ 和 artist_ 参数，你不能使用 assignment operator.

编译器也不会生成assignment operator。由于 assignment operator 的目的是在构造后更改成员，因此当其中一个成员永远无法更改时生成隐式 assignment operator 是没有意义的。编译器拒绝尝试猜测你想要它做什么，并强迫你提供你自己的 assignment operator 和你想要的语义。

我认为，相反，您可以使用 list::insert and list::erase 方法操作列表条目，如下所示，以获得您想要的结果。

for(auto itr = newSongList.begin(); itr != newSongList.end(); ++itr)
{

    for(auto jtr=itr; jtr != newSongList.begin(); --jtr){
        cout << itr->GetTitle() << " " << jtr->GetTitle() << endl;
        // if s1 is not before s2 then swap them
        if(!Song::CompareTitle(*itr, *jtr)){
            cout << "Swap True (" << itr->GetTitle() << "," << jtr->GetTitle() << " )"<< endl;
            Song i = Song(itr->GetTitle(),itr->GetArtist());
            Song j = Song(jtr->GetTitle(), jtr->GetArtist());

            newSongList.insert(itr, j); // extend list by inserting j song before itr song
            newSongList.erase(itr);     // itr is still pointing to original song
            newSongList.insert(jtr, i); // extend list by inserting i song before jtr song
            newSongList.erase(jtr);     // jtr is still pointing to original song

            cout << "Swap After (" << jtr->GetTitle() << "," << itr->GetTitle() << endl;
        }
    }
}

插入排序：我做错了什么？

Insertion Sort: What am I doing Wrong?

c++

insertion-sort