How to Search by Value in a Map

The C++ STL (Standard Template Library) includes maps. Maps are associative containers that hold sorted key-value pairs, each of which is identical and can be added or removed but not changed. It is possible to alter the values associated with keys.

Given a map and value, the task is to print all the keys which are having giving value.

Examples:

Example 1:

Input:

map={ { "this", 100 }, { "is", 200 }, { "BTech", 100 }, { "Geeks", 100 } }  value =100

Output:

BTech Geeks this

Example 2:

Input:

map={ { "this", 200 }, { "is", 200 }, { "BTech", 100 }, { "Geeks", 100 } }  value =200

Output:

this is

Search by value in Map

The objective is to go through the given map and print all of the key values that are mapped to given value. The loop that was used to find all of the key values is shown below.

for(auto &itr : given_Map) { 
if(itr.second == value) { 
print(itr.first) 
} 
}

If there is no key with the given value then print “Not Found”
Below is the implementation:

#include <bits/stdc++.h>
using namespace std;
int main()
{
    map<string, int> given_Map;

    // Givenmap
    given_Map["this"] = 100;
    given_Map["is"] = 200;
    given_Map["BTech"] = 100;
    given_Map["Geeks"] = 100;

    // Given value
    int value = 100;
    // let us take a boolean value which gives false when
    // any key is  found
    bool found = true;

    // Traverse the map
    for (auto& itr : given_Map) {

        // if the map value is equal to given value then
        // print the key
        // and set boolean value to false
        if (itr.second == value) {
            cout << itr.first << " ";
            found = false;
        }
    }

    // if there are no keys then print not found
    if (found == true) {
        cout << "No key found with given value";
    }
    return 0;
}

Output:

BTech Geeks this

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