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Java-based LeetCode algorithm problem solutions, regularly updated

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2721\. Execute Asynchronous Functions in Parallel

Medium

Given an array of asynchronous functions `functions`, return a new promise `promise`. Each function in the array accepts no arguments and returns a promise.

`promise` resolves:

*   When all the promises returned from `functions` were resolved successfully. The resolved value of `promise` should be an array of all the resolved values of promises in the same order as they were in the `functions`.

`promise` rejects:

*   When any of the promises returned from `functions` were rejected. `promise` should also reject with the reason of the first rejection.

Please solve it without using the built-in `Promise.all` function.

**Example 1:**

**Input:** 

    functions = [ 
        () => new Promise(resolve => setTimeout(() => resolve(5), 200)) 
    ]

**Output:** {"t": 200, "resolved": [5]}

**Explanation:** promiseAll(functions).then(console.log); // [5] The single function was resolved at 200ms with a value of 5.

**Example 2:**

**Input:** 
    
    functions = [ 
        () => new Promise(resolve => setTimeout(() => resolve(1), 200)), 
        () => new Promise((resolve, reject) => setTimeout(() => reject("Error"), 100)) 
    ]

**Output:** {"t": 100, "rejected": "Error"}

**Explanation:** Since one of the promises rejected, the returned promise also rejected with the same error at the same time.

**Example 3:**

**Input:** 
    
    functions = [ 
        () => new Promise(resolve => setTimeout(() => resolve(4), 50)), 
        () => new Promise(resolve => setTimeout(() => resolve(10), 150)), 
        () => new Promise(resolve => setTimeout(() => resolve(16), 100)) 
    ]

**Output:** {"t": 150, "resolved": [4, 10, 16]}

**Explanation:** All the promises resolved with a value. The returned promise resolved when the last promise resolved.

**Constraints:**

*   `functions is an array of functions that returns promises`
*   `1 <= functions.length <= 10`