map find() function in C++ STL

The map::find() is a built-in function in C++ STL which returns an iterator or a constant iterator that refers to the position where the key is present in the map. If the key is not present in the map container, it returns an iterator or a constant iterator which refers to map.end().

Syntax:

iterator map_name.find(key)
        or 
constant iterator map_name.find(key)

Parameters: The function accepts one mandatory parameter key which specifies the key to be searched in the map container.

Return Value: The function returns an iterator or a constant iterator which refers to the position where the key is present in the map. If the key is not present in the map container, it returns an iterator or a constant iterator which refers to map.end().

Time Complexity for Searching element :
Time complexity for searching elements in std::map is O(log n). Even in worst case it will be O(log n) because elements are stored internally as Balanced Binary Search tree (BST) whereas, in std::unordered_map best case time complexity for searching is O(1).



Below is the illustration of above function:

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// C++ program for illustration
// of map::find() function
#include <bits/stdc++.h>
using namespace std;
  
int main()
{
  
    // initialize container
    multimap<int, int> mp;
  
    // insert elements in random order
    mp.insert({ 2, 30 });
    mp.insert({ 1, 40 });
    mp.insert({ 3, 20 });
    mp.insert({ 4, 50 });
  
    cout << "The elements from position 3 in map are : \n";
    cout << "KEY\tELEMENT\n";
  
    // find() function finds the position at which 3 is
    for (auto itr = mp.find(3); itr != mp.end(); itr++)
        cout << itr->first
             << '\t' << itr->second << '\n';
  
    return 0;
}

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Output:

The elements from position 3 in map are : 
KEY    ELEMENT
3    20
4    50

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