Check if a key is present in a C++ map or unordered_map
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 notstring check_key(map<int, int> m, int key){ // Key is not present if (m.find(key) == m.end()) return "Not Present"; return "Present";}// Driverint 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 notstring check_key(unordered_map<int, int> m, int key){ // Key is not present if (m.find(key) == m.end()) return "Not Present"; return "Present";}// Driverint 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";}// Driverint 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";}// Driverint 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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