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In C++, RAII ties a resource to an object's lifetime: the resource is released automatically when the object goes out of scope. Objects in the same scope are destroyed in reverse order of creation.
Process the events in order:
{: enter a new inner scope.}: leave the current scope; every resource acquired in it is released, newest first.acquire <name>: create a resource in the current scope.
When the events run out, the remaining open scopes end from the innermost to the outermost (the program's outer scope included), releasing their resources the same way.
Implement raii_release_order(events).
Input
events: The events. Braces are balanced or left open, never closed without being opened.
Output
Return the resource names in the order they are released.
Constraints
0 ≤ number of events ≤ 100,000
Names have 1 to 20 characters without spaces
Examples
Example 1
Input:
events = ["acquire db", "{", "acquire file", "acquire lock", "}", "acquire log"]
Expected output:
["lock", "file", "log", "db"]Explanation
Leaving the inner scope releases lock then file (newest first). At the end the outer scope releases log then db: ["lock", "file", "log", "db"].
Example 2
Input:
events = ["{", "acquire a", "{", "acquire b"]
Expected output:
["b", "a"]Explanation
Two scopes are still open at the end: the innermost releases b, then the next releases a: ["b", "a"].
References
-
Example 1 Not runInput:
events = ["acquire db", "{", "acquire file", "acquire lock", "}", "acquire log"]Expected output:["lock", "file", "log", "db"]Your output -
Example 2 Not runInput:
events = ["{", "acquire a", "{", "acquire b"]Expected output:["b", "a"]Your output
4 hidden tests also run when you submit.
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💡 C++ Basics & Examples You Can Try Above
1. Declaring Variables and Constants
C++ requires you to declare the type of each variable. Use const to define read-only values that cannot be changed after initialization.
int age = 30;
double pi = 3.14159;
char grade = 'A';
std::string name = "Alice";
bool isActive = true;
// Constants
const int MAX_USERS = 100;
const std::string COMPANY = "CodeUtility";
// Attempting to modify a const will cause a compile-time error
// MAX_USERS = 200; // ❌ error
2. Conditionals (if / switch)
Use if, else if, else for branching. Use switch for multiple values.
int x = 2;
if (x == 1) {
std::cout << "One\n";
} else if (x == 2) {
std::cout << "Two\n";
} else {
std::cout << "Other\n";
}
// Switch-case
switch (x) {
case 1:
std::cout << "One\n";
break;
case 2:
std::cout << "Two\n";
break;
default:
std::cout << "Other\n";
}3. Loops
Use for, while, and do-while to repeat code blocks.
for (int i = 0; i < 3; i++) {
std::cout << i << "\n";
}
int n = 3;
while (n > 0) {
std::cout << n << "\n";
n--;
}4. Arrays
Arrays store multiple elements of the same type.
int numbers[3] = {10, 20, 30};
std::cout << numbers[1] << "\n";5. Array/Vector Manipulation
Use std::vector for dynamic arrays.
#include <vector>
std::vector nums = {1, 2, 3};
nums.push_back(4);
nums.pop_back();
for (int n : nums) {
std::cout << n << " ";
} 6. Console Input/Output
Use std::cin for input and std::cout for output.
std::string name;
std::cout << "Enter your name: ";
std::cin >> name;
std::cout << "Hello, " << name << "\n";7. Functions
Functions group reusable logic. Use parameters and return types.
int add(int a, int b) {
return a + b;
}
std::cout << add(3, 4);8. Maps
std::map stores key-value pairs like dictionaries.
#include <map>
std::map ages;
ages["Alice"] = 30;
std::cout << ages["Alice"]; 9. Exception Handling
Use try and catch to handle runtime errors.
try {
throw std::runtime_error("Error occurred");
} catch (const std::exception& e) {
std::cout << e.what();
}10. File I/O
Use fstream to read from and write to files.
#include <fstream>
std::ofstream out("file.txt");
out << "Hello File";
out.close();
std::ifstream in("file.txt");
std::string line;
getline(in, line);
std::cout << line;
in.close();11. String Manipulation
C++ strings support methods like length(), substr(), and find().
std::string text = "Hello World";
std::cout << text.length();
std::cout << text.substr(0, 5);
std::cout << text.find("World");12. Classes & Objects
C++ supports object-oriented programming using classes.
class Person {
public:
std::string name;
Person(std::string n) : name(n) {}
void greet() { std::cout << "Hi, I'm " << name; }
};
Person p("Alice");
p.greet();13. Pointers
A pointer stores the memory address of another variable. Use & to get an address,
and * to dereference (access the value at the address).
int x = 10;
int* ptr = &x;
std::cout << "Value of x: " << x << "\n";
std::cout << "Address of x: " << ptr << "\n";
std::cout << "Value from pointer: " << *ptr << "\n";
// Modify x through pointer
*ptr = 20;
std::cout << "Updated x: " << x << "\n";🐞 How to Debug %{language} Code Online
Use the online %{language} debugger to find runtime and logic errors without installing a compiler or desktop IDE. Server mode compiles with debug symbols and runs the program under GDB.
- Set one or more breakpoints beside the line numbers.
- Select Debug to compile and pause at the first matching breakpoint.
- Inspect the current line, call stack, and variables.
- Use Continue, Step Over, Step Into, or Step Out to control execution.
- Select Stop to end the debugging session.
Start with a small reproducible example and place a breakpoint just before the value or control flow becomes unexpected.