Coding

2637. Promise Time Limit

2023-05-16 2 min read
#Javascript#Typescript
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題目敘述

Given an asyncronous function fn and a time t in milliseconds, return a new time limited version of the input function.

A time limited function is a function that is identical to the original unless it takes longer than t milliseconds to fullfill. In that case, it will reject with "Time Limit Exceeded". Note that it should reject with a string, not an Error.

Example 1

Input: fn = async (n) => { await new Promise(res => setTimeout(res, 100)); return n * n; } inputs = [5] t = 50 Output: {“rejected”:“Time Limit Exceeded”,“time”:50} Explanation: The provided function is set to resolve after 100ms. However, the time limit is set to 50ms. It rejects at t=50ms because the time limit was reached.

Example 2

Input: fn = async (n) => { await new Promise(res => setTimeout(res, 100)); return n * n; } inputs = [5] t = 150 Output: {“resolved”:25,“time”:100} Explanation: The function resolved 5 * 5 = 25 at t=100ms. The time limit is never reached.

Example 3

Input: fn = async (a, b) => { await new Promise(res => setTimeout(res, 120)); return a + b; } inputs = [5,10] t = 150 Output: {“resolved”:15,“time”:120} Explanation: The function resolved 5 + 10 = 15 at t=120ms. The time limit is never reached.

Example 4

Input: fn = async () => { throw “Error”; } inputs = [] t = 1000 Output: {“rejected”:“Error”,“time”:0} Explanation: The function immediately throws an error.

解題思路

Promise.race([arr]); : race 中的陣列哪一個 Function 先跑完，return 該 Function。

Solution

/**
 * @param {Function} fn
 * @param {number} t
 * @return {Function}
 */
var timeLimit = function(fn, t) {
	return async function(...args) {
        const timeout = new Promise((resolved, reject) => {
            setTimeout(() => reject("Time Limit Exceeded"), t);
        });
        return Promise.race([fn(...args), timeout]);
    }
};

/**
 * const limited = timeLimit((t) => new Promise(res => setTimeout(res, t)), 100);
 * limited(150).catch(console.log) // "Time Limit Exceeded" at t=100ms
 */

type Fn = (...params: any[]) => Promise<any>;

function timeLimit(fn: Fn, t: number): Fn {
	return async function(...args) {
        const timeout: Promise<any> = new Promise((resolved: any, reject: any) => {
            setTimeout(() => reject("Time Limit Exceeded"), t);
        });
        return Promise.race([fn(...args), timeout]);
    }
};

/**
 * const limited = timeLimit((t) => new Promise(res => setTimeout(res, t)), 100);
 * limited(150).catch(console.log) // "Time Limit Exceeded" at t=100ms
 */
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