Traversing a map (or unordered_map) in C++ STL

We can traverse map and unordered_map using following different ways.

Using a range based for loop

map

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// CPP program to traverse a map using range 
// based for loop
#include <bits/stdc++.h>
using namespace std;
  
int main()
{
    int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    map<int, int> m;
    for (int i = 0; i < n; i++)
        m[arr[i]]++;
  
    cout << "Element  Frequency" << endl;
    for (auto i : m)
        cout << i.first << "   " << i.second 
             << endl;
  
    return 0;
}

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// CPP program to traverse a unordered_map using  


// range based for loop 


#include <bits/stdc++.h> 


using namespace std; 


  


int main() 


{ 


    int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; 


    int n = sizeof(arr) / sizeof(arr[0]); 


  


    unordered_map<int, int> m; 


    for (int i = 0; i < n; i++) 


        m[arr[i]]++; 


  


    cout << "Element Frequency" << endl; 


    for (auto i : m) 


        cout << i.first << "    " << i.second 


             << endl; 


  


    return 0; 


} 



















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Output [NOTE: For unordered_map output rows can be

in any order]


        
          
          
          
        

            

Element  Frequency
1        4
2        1
3        2
4        1



 


Traversing using begin() and end()




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// CPP program to traverse a map using iterators 


#include <bits/stdc++.h> 


using namespace std; 


  


int main() 


{ 


    int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; 


    int n = sizeof(arr) / sizeof(arr[0]); 


  


    map<int, int> m; 


    for (int i = 0; i < n; i++) 


        m[arr[i]]++; 


  


    cout << " Element Frequency" << endl; 


    for (auto i = m.begin(); i != m.end(); i++) 


        cout << i->first << "      " << i->second 


             << endl; 


  


    return 0; 


} 



















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unordered_map














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// CPP program to traverse a unordered_map  


// using iterators 


#include <bits/stdc++.h> 


using namespace std; 


  


int main() 


{ 


    int arr[] = { 1, 1, 2, 1, 1, 3, 4, 3 }; 


    int n = sizeof(arr) / sizeof(arr[0]); 


  


    unordered_map<int, int> m; 


    for (int i = 0; i < n; i++) 


        m[arr[i]]++; 


  


    cout << " Element Frequency" << endl; 


    for (auto i = m.begin(); i != m.end(); i++) 


        cout << i->first << "       " << i->second  


             << endl; 


  


    return 0; 


} 



















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Output [NOTE: For unordered_map output rows can be

in any order]


Element  Frequency
1        4
2        1
3        2
4        1



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