michel's blog

Multimap?????
By michel, history, 9 years ago, In English

Can anybody tell me about C++ multimaps. As far as I know you can assign many values to a key but... how do I access to any of theese values?

  • Vote: I like it
  • 0
  • Vote: I do not like it

»
9 years ago, hide # |
 
Vote: I like it 0 Vote: I do not like it 
map<int,set<int, int> > m;
m[key].insert(values);
m[key].find(x)
→ Reply
  • »
    »
    9 years ago, hide # ^ |
    ← Rev. 3  
    Vote: I like it 0 Vote: I do not like it 
    Sorry but I dont get it yet.

    I mean for example:

    I have 1->2, 2->4, 1->3 and 3->5. That would be as:

    key |  values
   1|  {2,3}
   2|  {4}
   3|  {5}

    How can I know how many values are assigned to every key and how can I make reference to each of the values a key has?

    → Reply
»
9 years ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Thanks two of you for help

→ Reply
  • »
    »
    9 years ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    Unfortunately they didn't tell you how to use multimap. Here's an example.

    → Reply
    • »
      »
      »
      9 years ago, hide # ^ |
       
      Vote: I like it 0 Vote: I do not like it

      That's true, their comments were helpful but what i wanted was an example of using multimap. Could you make a comment with the example, my internet provider does not allow me to go that link

      → Reply
      • »
        »
        »
        »
        9 years ago, hide # ^ |
         
        Vote: I like it 0 Vote: I do not like it 
        #include <map>
#include<iostream>
using namespace std;
int main() {
	multimap<int,string> m;
	m.insert({1,"hello"});
	m.insert({1,"world"});
	m.insert({2,"goodbye"});
	m.insert({3,"spacecows"});
	
	cout<<"Number of elements in key 1: "<<m.count(1)<<endl;
	
	auto range = m.equal_range(1);
	for(auto iter = range.first; iter != range.second; iter++) cout<<iter->second<<" ";
	cout<<endl;
	return 0;
}
        → Reply
        • »
          »
          »
          »
          »
          9 years ago, hide # ^ |
           
          Vote: I like it 0 Vote: I do not like it

          I see, very ilustrative example. I've never used auto I gess it make the variable get the type that is asigned to it, am I right?

          → Reply
          • »
            »
            »
            »
            »
            »
            9 years ago, hide # ^ |
             
            Vote: I like it 0 Vote: I do not like it

            Yes, the compiler will deduce the type for you. auto is quite a bit shorter to write than pair<multimap<int,string>::iterator,multimap<int,string>::iterator>.

            I recommend reading these two posts (C++11 for programming contests... and C++ Tricks) for some additional info on using C++11 in programming contests.

            → Reply