LeetCode 2721: Execute Asynchronous Functions in Parallel Solution

Master LeetCode problem 2721 (Execute Asynchronous Functions in Parallel), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2721. Execute Asynchronous Functions in Parallel

Medium

Problem Explanation

Explanation

To solve this problem, we need to execute all the asynchronous functions in the given array in parallel and return a new promise that resolves when all the promises returned by the functions are resolved successfully or rejects if any of the promises is rejected.

We will create a new promise and iterate over the array of functions. For each function, we will execute it and store the promise in an array. We will keep track of the number of resolved promises and the first rejection if any. Once all promises are settled, we will resolve the new promise with the resolved values or reject it with the first rejection reason.

Time complexity: O(n), where n is the number of functions in the input array.
Space complexity: O(n) for storing promises.

Solution Code

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;

public class Solution {
    public CompletableFuture<List<Object>> promiseAll(List<Runnable> functions) {
        CompletableFuture<Void>[] futures = functions.stream()
                .map(func -> CompletableFuture.runAsync(func))
                .toArray(CompletableFuture[]::new);

        return CompletableFuture.allOf(futures)
                .thenApply(ignored -> {
                    List<Object> results = new ArrayList<>();
                    for (CompletableFuture<Void> future : futures) {
                        results.add(future.getNow(null));
                    }
                    return results;
                });
    }
}

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