如何在C ++中使用堆栈，队列或BST对文件中的记录进行排序？

Question

If you have a .dat file with records such as:

805816899 Andrew
803975268 Bob
912684297 Jeff
123546789 Louis
751354687 Kevin

What would be the easiest data structure to use in order to sort the list by ID number and then write to screen? I figure a BST would make the most sense and be the most efficient, but a stack would be easier and faster when dealing with a small file such as this.

Also, how would you implement it?

Answer 1

The simplest was to sort them using a BST would be to put them in an std::map<int, std::string> . This is a self sorted data structure using a BST internally (although that isn't explicitly specified by the standard). If you do not want look-up, you can use an std::set of a user defined type instead (see next paragraph).

If you want to store them in a flat array-like structure, you could create a small struct to hold the information, store instances of it in an std::vector , and use a suitable comparison function in combination with std::sort to do the sorting.

BST:

#include <string>
#include <map>
std::map<int, std::string> m;
m[805816899] = "Andrew";
m[803975268] = "Bob";

and so on.

array-like solution:

struct Foo 
{ 
  Foo(int ID, const std::string& name) : ID(ID), name(name) {}
  int ID; 
  std::string name;
};
// comparison for sorting
bool comp(const Foo& lhs, const Foo& rhs) { return lhs.ID < rhs.ID; }

#include <vector>
#include <algorithm>
....
std::vector<Foo> v;
v.push_back(Foo(805816899, "Andrew"));
v.push_back(Foo(803975268, "Bob"));
// add more entries
std::sort(v.begin(), v.end(), comp);

Answer 2

I think, a trie is the easiest way to implement the whole sorting and it's O(n) if the length of the id is constant.

#include <iostream>
#include <cassert>
#include <string>

class node {
  bool final;
  union {
    node *next[10];
    char *name;
  };
  node *get_at(int index)
  {
    assert(!final);
    return next[index] ? next[index] : (next[index] = new node);
  }

public:
  node() : final(false) { std::fill(next, next+10, (node*)0); }
  ~node() {
    if (final)
      delete name;
    else
      for (int i=0; i<10; ++i)
        delete next[i];
  }

  void insert(const char *id, std::string const& s)
  {
    if (*id) {
      get_at(*id - '0')->insert(id+1, s);
    } else {
      final=true;
      name = new char[s.size()+1]();
      std::copy(s.begin(), s.end(), name);
    }
  }

  void print_all(std::ostream& os) const
  {
    if (final)
      os << name << '\n';
    else
      for (int i = 0; i < 10; ++i)
        if (next[i])
          next[i]->print_all(os);
  }
};

int main()
{
  node top;
  for (std::string id, name; std::cin >> id >> name;)
    top.insert(id.c_str(), name);
  top.print_all(std::cout);
}