Retry a Failing Operation

medium Exception Handling

An operation fails the first a times it is called and then works. You may call it at most b times. Print success after N attempts if it works (N is the number of calls), or failed after b attempts if all b calls fail. Use exception handling inside a loop.

Constraints

0 <= a <= 10^4
1 <= b <= 10^4

Examples

Input

2 3

Output

success after 3 attempts

Input

3 3

Output

failed after 3 attempts

try-catch in a loop
Retry pattern
Bounded attempts

Solutions

Best approachTime O(b)Space O(1)

A retry loop puts try-catch inside the loop. Success returns at once; a failure falls through to the next attempt. Real code also waits between attempts and limits the attempts, as here.

Same code works in Java810172125Basic features only, so nothing changes between versions.

/*
 * Problem : Retry.
 * Input   : Two integers: failures and maximum attempts.
 * Output  : The result text.
 * Approach: Loop with try-catch.
 * Time    : O(b)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // Step 1: This helper simulates the operation. It throws an exception while "failuresLeft" is above 0.
        static void operation(long call, long failures) {
            if (call <= failures) {
                throw new IllegalStateException("temporary failure");
            }
        }

    // This method solves the task. It receives the input and returns the answer.
    static String solve(long a, long b) {
        // Step 2: Try the operation again and again, but not more than b times.
        for (long attempt = 1; attempt <= b; attempt++) {
            try {
                operation(attempt, a);
                // Step 3: No exception means success. Stop at once.
                return "success after " + attempt + " attempts";
            } catch (IllegalStateException error) {
                // Step 4: The call failed. The loop tries again.
            }
        }
        return "failed after " + b + " attempts";
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        long b = scanner.nextLong();
        System.out.println(solve(a, b));
    }
}

Hints (1)

Where do the try and catch go: inside or outside the loop?