Map

A map stores the values organized by keys. Unlike a set, a map has a dedicated key per value.  Maps generally use a red-black tree as an internal data structure, which is a balanced BST that guarantees O( log N ) runtime efficiency for searching or locating a value in the map. The values stored in a map are sorted based on the key, using a red-black tree. The keys used in a map must be unique. A map will not retain the sequences of the input as it reorganizes the values based on the key, that is, the red-black tree will be rotated to balance the red-black tree height.

Let's write a simple program to understand map usage:

#include <iostream>
#include <map>
#include <iterator>
#include <algorithm>
using namespace std;

int main ( ) {

  map<string, long> contacts;

  contacts["Jegan"] = 123456789;
  contacts["Meena"] = 523456289;
  contacts["Nitesh"] = 623856729;
  contacts["Sriram"] = 993456789;

  auto pos = contacts.find( "Sriram" );

  if ( pos != contacts.end() )
    cout << pos->second << endl;

  return 0;
}

Let's compile and check the output of the program:

g++ main.cpp -std=c++17
./a.out

The output is as follows:

Mobile number of Sriram is 8901122334