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how to initialize unordered_map c++

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Sahil choudhary answered on April 10, 2022 Popularity 9/10 Helpfulness 4/10

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how to initialize unordered_map c++

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  unordered_map<string, string>New_map;
   
    // Adding key-value pairs using
    // Initializer list
    New_map = {{"Ground", "Grass"},
               {"Floor", "Cement"},
               {"Table", "Wood"}};

//Source www.geeksforgeeks.org

Popularity 9/10 Helpfulness 4/10 Language cpp

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Tags: c++

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Contributed on Dec 14 2022

Sahil choudhary

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initialize unordered_map c++

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unordered_map<int, string> m =
    {
        {1, "one"},
        {2, "two"},
        {3, "three"}
    };
C++Copy

Popularity 9/10 Helpfulness 5/10 Language cpp

Source: iq.opengenus.org

Tags: c++

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Contributed on Sep 06 2022

Super Squirrel

0 Answers Avg Quality 2/10

unordered_map

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unordered_map vs map : 
map (like set) is an ordered sequence of unique keys whereas in unordered_map key can be stored in any order, so unordered. 
The map is implemented as a balanced tree structure that is why it is possible to maintain order between the elements (by specific tree traversal).
The time complexity of map operations is O(log n) while for unordered_map, it is O(1) on average. 


at():        This function in C++ unordered_map returns the reference to the value with the element as key k.
begin():     Returns an iterator pointing to the first element in the container in the unordered_map container
end():       Returns an iterator pointing to the position past the last element in the container in the unordered_map container
bucket():    Returns the bucket number where the element with the key k is located in the map.
bucket_count:bucket_count is used to count the total no. of buckets in the unordered_map. No parameter is required to pass into this function.
bucket_size: Returns the number of elements in each bucket of the unordered_map.
count():    Count the number of elements present in an unordered_map with a given key.
equal_range: Return the bounds of a range that includes all the elements in the container with a key that compares equal to k.
find():      Returns iterator to element.
empty():     checks whether container is empty in the unordered_map container.
erase():     erase elements in the container in the unordered_map container.

Popularity 10/10 Helpfulness 4/10 Language cpp

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Contributed on Jun 13 2022

Sleepy Head

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unordered_map c++

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#include <iostream>
#include <unordered_map>
using namespace std;
int main()
{
    unordered_map<string, int> umap;
    // inserting values by using [] operator
    umap["GeeksforGeeks"] = 10;
    umap["Practice"] = 20;
    umap["Contribute"] = 30;
    // Traversing an unordered map
    for (auto x : umap)
      cout << x.first << " " << x.second << endl;
}

Popularity 10/10 Helpfulness 4/10 Language cpp

Source: www.geeksforgeeks.org

Tags: c++

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Contributed on Oct 12 2022

Old-fashioned Otter

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unordered_map c++

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#include <iostream>
#include <unordered_map>
using namespace std;
int main()
{
    unordered_map<string, int> umap;
    // inserting values by using [] operator
    umap["GeeksforGeeks"] = 10;
    umap["Practice"] = 20;
    umap["Contribute"] = 30;
    // Traversing an unordered map
    for (auto x : umap)
      cout << x.first << " " << x.second << endl;
}

Popularity 9/10 Helpfulness 3/10 Language cpp

Source: www.geeksforgeeks.org

Tags: c++

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Contributed on Oct 12 2022

Old-fashioned Otter

0 Answers Avg Quality 2/10

unordered_map in c++

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// C++ program to demonstrate functionality of unordered_map
#include <iostream>
#include <unordered_map>
using namespace std;
  
int main()
{
    // Declaring umap to be of <string, int> type
    // key will be of string type and mapped value will
    // be of int type
    unordered_map<string, int> umap;
  
    // inserting values by using [] operator
    umap["GeeksforGeeks"] = 10;
    umap["Practice"] = 20;
    umap["Contribute"] = 30;
  
    // Traversing an unordered map
    for (auto x : umap)
      cout << x.first << " " << x.second << endl;
  
}

Popularity 10/10 Helpfulness 2/10 Language cpp

Source: www.geeksforgeeks.org

Tags: c++

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Contributed on Jun 08 2022

Dead Dragonfly

0 Answers Avg Quality 2/10

unordered_map in c++

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// C++ program to demonstrate
// Initialization, indexing,
// and iteration
#include <iostream>
#include <unordered_map>
using namespace std;
 
// Driver code
int main()
{
  // Declaring umap to be of
  // <string, double> type key
  // will be of string type and
  // mapped value will be of double type
  unordered_map<string, double> umap;
 
  // inserting values by using [] operator
  umap["PI"] = 3.14;
  umap["root2"] = 1.414;
  umap["root3"] = 1.732;
  umap["log10"] = 2.302;
  umap["loge"] = 1.0;
 
  // inserting value by insert function
  umap.insert(make_pair("e", 2.718));
 
  string key = "PI";
 
  // If key not found in map iterator
  // to end is returned
  if (umap.find(key) == umap.end())
    cout << key << " not found\n\n";
   
  // If key found then iterator to that
  // key is returned
  else
    cout << "Found " << key << "\n\n";
   
  key = "lambda";
  if (umap.find(key) == umap.end())
    cout << key << " not found\n";
  else
    cout << "Found " << key << endl;
   
  // iterating over all value of umap
  unordered_map<string, double>::iterator itr;
  cout << "\nAll Elements : \n";
  for (itr = umap.begin();
       itr != umap.end(); itr++)
  {
    // itr works as a pointer to
    // pair<string, double> type
    // itr->first stores the key part and
    // itr->second stores the value part
    cout << itr->first << "  " <<
            itr->second << endl;
  }
}

Popularity 9/10 Helpfulness 2/10 Language cpp

Source: www.geeksforgeeks.org

Tags: c++

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Contributed on Nov 27 2022

Darshan Trivedi

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c++ unordered_map initialize new value

Comment

unordered_map<string, int> demo; 
demo["abc"] = 1;

Popularity 9/10 Helpfulness 1/10 Language cpp

Source: iq.opengenus.org

Tags: c++

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Contributed on Apr 10 2022

SharxNZ

0 Answers Avg Quality 2/10

how to initialize unordered_map c++

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