MaxWelll's blog

Multimap?????
By MaxWelll, history, 8 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?

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8 years ago, # |
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map<int,set<int, int> > m;
m[key].insert(values);
m[key].find(x)
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    8 years ago, # ^ |
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    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?

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      8 years ago, # ^ |
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      l = m.lower_bound(key);
      u = m.upper_bound(key);
      c = std::distance(l, u);

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8 years ago, # |
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Thanks two of you for help

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    8 years ago, # ^ |
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    Unfortunately they didn't tell you how to use multimap. Here's an example.

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      8 years ago, # ^ |
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      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

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        8 years ago, # ^ |
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        #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;
}
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          8 years ago, # ^ |
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          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?

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            8 years ago, # ^ |
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            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.

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