Check if a key is present in a C++ map or unordered_map (original) (raw)

Last Updated : 30 Apr, 2024

A C++ map and unordered_map are initialized to some keys and their respective mapped values.
Examples:

**Input :
Map : 1 -> 4, 2 -> 6, 4 -> 6
Check1 : 5, Check2 : 4
**Output : 5 : Not present, 4 : Present

C++ implementation :

map `

// CPP code to check if a // key is present in a map #include <bits/stdc++.h> using namespace std;

// Function to check if the key is present or not string check_key(map<int, int> m, int key) { // Key is not present if (m.find(key) == m.end()) return "Not Present";

return "Present";

}

// Driver int main() { map<int, int> m;

// Initializing keys and mapped values
m[1] = 4;
m[2] = 6;
m[4] = 6;

// Keys to be checked
int check1 = 5, check2 = 4;

// Function call
cout << check1 << ": " << check_key(m, check1) << '\n';
cout << check2 << ": " << check_key(m, check2);

}

unordered\_map

// CPP code to check if a key is present // in an unordered_map #include <bits/stdc++.h> using namespace std;

// Function to check if the key is present or not string check_key(unordered_map<int, int> m, int key) { // Key is not present if (m.find(key) == m.end()) return "Not Present";

return "Present";

}

// Driver int main() { unordered_map<int, int> m;

// Initialising keys and mapped values
m[1] = 4;
m[2] = 6;
m[4] = 6;

// Keys to be checked
int check1 = 5, check2 = 4;

// Function call
cout << check1 << ": " << check_key(m, check1) << '\n';
cout << check2 << ": " << check_key(m, check2);

}

`

Output:

5: Not Present
4: Present

**Approach 2nd:

we can also use the count function of the map in c++.

**Implementation:

**1. Map

C++ `

// CPP code to check if a // key is present in a map #include <bits/stdc++.h> using namespace std;

// Function to check if the key is present or not using count() string check_key(map<int, int> m, int key) { // Key is not present if (m.count(key) == 0) return "Not Present";

return "Present";

}

// Driver int main() { map<int, int> m;

// Initializing keys and mapped values
m[1] = 4;
m[2] = 6;
m[4] = 6;

// Keys to be checked
int check1 = 5, check2 = 4;

// Function call
cout << check1 << ": " << check_key(m, check1) << '\n';
cout << check2 << ": " << check_key(m, check2);

}

`

**Output:

5: Not Present

4: Present

**2. Unordered Map

C++ `

// CPP code to check if a key is present // in an unordered_map #include <bits/stdc++.h> using namespace std;

// Function to check if the key is present or not using count() string check_key(unordered_map<int, int> m, int key) { // Key is not present if (m.count(key) == 0) return "Not Present";

return "Present";

}

// Driver int main() { unordered_map<int, int> m;

// Initialising keys and mapped values
m[1] = 4;
m[2] = 6;
m[4] = 6;

// Keys to be checked
int check1 = 5, check2 = 4;

// Function call
cout << check1 << ": " << check_key(m, check1) << '\n';
cout << check2 << ": " << check_key(m, check2);

}

`

**Output:

5: Not Present

4: Present