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How to Solve Design Cancellable Function Problem
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LeetCode ProblemDesign Cancellable Function
Sometimes you have a long running task, and you may wish to cancel it before it completes. To help with this goal, write a function cancellable that accepts a generator object and returns an array of two values: a cancel function and a promise. You may assume the generator function will only yield promises. It is your function's responsibility to pass the values resolved by the promise back to the generator. If the promise rejects, your function should throw that error back to the generator. If the cancel callback is called before the generator is done, your function should throw an error back to the generator. That error should be the string "Cancelled" (Not an Error object). If the error was caught, the returned promise should resolve with the next value that was yielded or returned. Otherwise, the promise should reject with the thrown error. No more code should be executed. When the generator is done, the promise your function returned should resolve the value the generator returned. If, however, the generator throws an error, the returned promise should reject with the error. An example of how your code would be used: If instead cancel() was not called or was called after t=100ms, the promise would have resolved 5.
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Problem Breakdown
Understanding the Design Cancellable Function Problem
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Problem Statement
Sometimes you have a long running task, and you may wish to cancel it before it completes. To help with this goal, write a function cancellable that accepts a generator object and returns an array of two values: a cancel function and a promise. You may assume the generator function will only yield promises. It is your function's responsibility to pass the values resolved by the promise back to the generator. If the promise rejects, your function should throw that error back to the generator. If the cancel callback is called before the generator is done, your function should throw an error back to the generator. That error should be the string "Cancelled" (Not an Error object). If the error was caught, the returned promise should resolve with the next value that was yielded or returned. Otherwise, the promise should reject with the thrown error. No more code should be executed. When the generator is done, the promise your function returned should resolve the value the generator returned. If, however, the generator throws an error, the returned promise should reject with the error. An example of how your code would be used: If instead cancel() was not called or was called after t=100ms, the promise would have resolved 5.
HardProblem #2650
LeetCodeDesign Cancellable Function
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Examples
# Example 1
Input
—
Output
—
# Example 2
Input
generatorFunction = function*() { return 42; } cancelledAt = 100Output
{"resolved": 42}# Example 3
Input
generatorFunction = function*() { const msg = yield new Promise(res => res("Hello")); throw `Error: ${msg}`; } cancelledAt = nullOutput
{"rejected": "Error: Hello"}# Example 4
Input
generatorFunction = function*() { yield new Promise(res => setTimeout(res, 200)); return "Success"; } cancelledAt = 100Output
{"rejected": "Cancelled"}# Example 5
Input
generatorFunction = function*() { let result = 0; yield new Promise(res => setTimeout(res, 100)); result += yield new Promise(res => res(1)); yield new Promise(res => setTimeout(res, 100)); result += yield new Promise(res => res(1)); return result; } cancelledAt = nullOutput
{"resolved": 2}# Example 6
Input
generatorFunction = function*() { let result = 0; try { yield new Promise(res => setTimeout(res, 100)); result += yield new Promise(res => res(1)); yield new Promise(res => setTimeout(res, 100)); result += yield new Promise(res => res(1)); } catch(e) { return result; } return result; } cancelledAt = 150Output
{"resolved": 1}# Example 7
Input
generatorFunction = function*() { try { yield new Promise((resolve, reject) => reject("Promise Rejected")); } catch(e) { let a = yield new Promise(resolve => resolve(2)); let b = yield new Promise(resolve => resolve(2)); return a + b; }; } cancelledAt = nullOutput
{"resolved": 4}Constraints
cancelledAt == null or 0 <= cancelledAt <= 1000
generatorFunction returns a generator object
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Solve Design Cancellable Function — Sometimes you have a long running task, and you may wish to cancel it before it ...
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def solve(input):
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Time: O(n) | Space: O(n)
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Phantom Code catches common mistakes like off-by-one errors, missing edge cases, incorrect base conditions, and suboptimal approaches. It provides clean, well-structured code that handles all edge cases.
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