Check if a key is present in a C++ map or unordered_map
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
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