C++ Unordered_map Library - insert() Function


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Description

The C++ function std::unordered_map::insert() extends container by inserting new elements in the unordered_map.

Declaration

Following is the declaration for std::unordered_map::insert() function form std::unordered_map header.

C++11

template <class InputIterator>
void insert (InputIterator first,InputIterator last);

Parameters

  • first − Input iterator to the initial position in range.

  • last − Input iterator to the final position in range.

Return value

None

Time complexity

Linear i.e. O(n) in average case.

Quadratic i.e. O(N * (size+ 1)) in worst case.

Example

The following example shows the usage of std::unordered_map::insert() function.

#include <iostream>
#include <unordered_map>

using namespace std;

int main(void) {
   unordered_map<char, int> um1 = {
            {'a', 1},
            {'b', 2},
            {'c', 3},
            {'d', 4},
            {'e', 5},
            };

   unordered_map<char, int> um2;

   um2.insert(um1.begin(), um1.end());

   cout << "Unordered map contains following elements" << endl;

   for (auto it = um2.begin(); it != um2.end(); ++it)
      cout << it->first << " = " << it->second << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Unordered map contains following elements
d = 4
c = 3
b = 2
a = 1
e = 5
unordered_map.htm
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