docs(cpp): add reserve() entry for unordered_map #7144

content/cpp/concepts/unordered-map/terms/reserve/reserve.md

@@ -0,0 +1,104 @@
+---
+Title: '.reserve()'
+Description: 'Reserves space for at least the specified number of elements in an unordered map.'
+Subjects:
+  - 'Computer Science'
+  - 'Game Development'
+Tags:
+  - 'Classes'
+  - 'Map'
+  - 'Memory'
+  - 'Objects'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+The **`.reserve()`** method reserves space for at least the specified number of elements in an [unordered map](https://www.codecademy.com/resources/docs/cpp/unordered-map), helping optimize performance by reducing costly rehash operations during bulk insertions.
+
+## Syntax
+
+```pseudo
+mapName.reserve(count);
+```
+
+**Parameters:**
+
+- `count`: The minimum number of elements to reserve space for.
+
+**Return value:**
+
+This is a `void` method. It doesn’t return a value but affects the internal capacity of the unordered map.
+
+## Example
+
+The following example demonstrates the use of the `.reserve()` method with an unordered map to optimize performance when adding student grades:
+
+```cpp
+#include <iostream>
+#include <unordered_map>
+
+int main() {
+  // Initializing unordered_map and reserving space for 10 elements
+  std::unordered_map<std::string, int> studentGrades;
+  studentGrades.reserve(10);
+
+  // Adding student grades
+  studentGrades["Alice"] = 95;
+  studentGrades["Bob"] = 87;
+  studentGrades["Charlie"] = 92;
+  studentGrades["Diana"] = 88;
+
+  std::cout << "Student grades after reservation:\n";
+  for (const auto& student : studentGrades) {
+    std::cout << student.first << ": " << student.second << std::endl;
+  }
+
+  std::cout << "Bucket count: " << studentGrades.bucket_count() << std::endl;
+
+  return 0;
+}
+```
+
+This example results in the following output:
+
+```shell
+Student grades after reservation:
+Charlie: 92
+Bob: 87
+Diana: 88
+Alice: 95
+Bucket count: 11
+```
+
+## Codebyte Example
+
+The following codebyte example demonstrates the use of the `.reserve()` method with an unordered map to store employee information efficiently:
+
+```codebyte/cpp
+#include <iostream>
+#include <unordered_map>
+
+int main() {
+  // Initializing unordered_map with employee IDs and names
+  std::unordered_map<int, std::string> employees;
+
+  // Reserve space for 8 employees to optimize performance
+  employees.reserve(8);
+
+  // Adding employee data
+  employees[101] = "John";
+  employees[102] = "Sarah";
+  employees[103] = "Mike";
+  employees[104] = "Emma";
+
+  std::cout << "Employee roster:\n";
+  for (const auto& emp : employees) {
+    std::cout << "ID " << emp.first << ": " << emp.second << std::endl;
+  }
+
+  std::cout << "Reserved bucket count: " << employees.bucket_count() << std::endl;
+
+  return 0;
+}
+```