Add function contains() to map data structure

map/contains.md

@@ -0,0 +1,28 @@
+# contains
+
+**Description :**  This method is available since C++20 and checks if there is an element with a specific key in the map container. Returns true if an element is found, otherwise returns false.
+
+**Example** :
+
+```cpp
+// C++ code to demonstrate working of map.contains()
+#include <iostream>
+#include <map>
+
+int main(){
+    // create 'example' map where 1 and 2 are keys, while a and b are values
+    std::map<int,char> example = {{1,'a'},{2,'b'}};
+    int key = 2;
+
+    // contains() will return true if the key was found, false if not
+    if(example.contains(key)){
+        std::cout << "Found key " << key << " with value " << example[key] << '\n';
+    }
+    else{
+        std::cout << "Key " << key << " not found in map\n";
+    }
+
+    return 0;
+}
+```
+**[Run Code](https://rextester.com/IYJR76647)**