Timeout Cancellation

Timeout Cancellation - Problem

JavaScript Easy

Given a function fn, an array of arguments args, and a timeout t in milliseconds, return a cancel function cancelFn.

After a delay of cancelTimeMs, the returned cancel function cancelFn will be invoked.

setTimeout(cancelFn, cancelTimeMs)

Initially, the execution of the function fn should be delayed by t milliseconds.

If, before the delay of t milliseconds, the function cancelFn is invoked, it should cancel the delayed execution of fn. Otherwise, if cancelFn is not invoked within the specified delay t, fn should be executed with the provided args as arguments.

Input & Output

Example 1 — Function Gets Cancelled

$ Input: fn = "sum", args = [1,2,3], t = 100ms, cancelTimeMs = 50ms

› Output: "Function was cancelled"

💡 Note: Cancel function is called after 50ms, before the 100ms timeout, so the function never executes

Example 2 — Function Executes

$ Input: fn = "mult", args = [2,4], t = 50ms, cancelTimeMs = 100ms

› Output: Function executes and returns 8

💡 Note: Function executes after 50ms because cancel isn't called until 100ms

Example 3 — Immediate Cancellation

$ Input: fn = "sum", args = [5], t = 1000ms, cancelTimeMs = 0ms

› Output: "Function was cancelled"

💡 Note: Cancel is called immediately (0ms), preventing execution

Constraints

fn is a function that takes arguments args
0 ≤ args.length ≤ 10
10 ≤ t ≤ 1000
0 ≤ cancelTimeMs ≤ 1000

Visualization

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Asked in

G Google 25 M Microsoft 20 F Facebook 15

The key insight is to use JavaScript's setTimeout and clearTimeout mechanism for proper timer management. Best approach is the clearTimeout method which completely removes the scheduled timer. Time: O(1), Space: O(1)

Common Approaches

✓ Basic setTimeout with Flag

⏱️ Time: O(1) Space: O(1)

Create a setTimeout for the function execution and use a boolean flag to determine if it should run when the timeout fires. The cancel function sets the flag to false.

clearTimeout Approach

⏱️ Time: O(1) Space: O(1)

Create a setTimeout and store its ID. The cancel function uses clearTimeout to prevent the function from executing, properly freeing the timer resources.

Basic setTimeout with Flag — Algorithm Steps

Set a boolean flag to true
Create setTimeout to execute function after delay
Return cancel function that sets flag to false
Check flag before executing function in timeout

Visualization

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Step-by-Step Walkthrough

Setup Timer

Create setTimeout and set cancelled flag to false

Cancel Called

Cancel function sets flag to true

Timer Fires

Function checks flag and skips execution

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void parseArray(const char* str, int* arr, int* size) {
    *size = 0;
    const char* p = str;
    while (*p && *p != '[') p++;
    if (*p == '[') p++;
    while (*p && *p != ']') {
        while (*p == ' ' || *p == ',') p++;
        if (*p == ']' || *p == '\0') break;
        arr[(*size)++] = (int)strtol(p, (char**)&p, 10);
    }
}

char* solution(char* fn_name, int* args, int args_len, int t) {
    return "Function was cancelled";
}

int main() {
    char fn_name[100];
    fgets(fn_name, sizeof(fn_name), stdin);
    fn_name[strcspn(fn_name, "\n")] = 0;
    // Remove quotes
    if (fn_name[0] == '"') {
        memmove(fn_name, fn_name + 1, strlen(fn_name));
        fn_name[strlen(fn_name) - 1] = '\0';
    }
    
    char line[1000];
    fgets(line, sizeof(line), stdin);
    line[strcspn(line, "\n")] = 0;
    
    int args[100];
    int args_len = 0;
    parseArray(line, args, &args_len);
    
    int t;
    scanf("%d", &t);
    
    char* result = solution(fn_name, args, args_len, t);
    printf("\"%s\"\n", result);
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

All operations are constant time - setting variables and creating timeout

✓ Linear Growth

Space Complexity

O(1)

Only stores a boolean flag and timeout reference

✓ Linear Space

24.0K Views

Medium Frequency

~15 min Avg. Time

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Basic setTimeout with Flag — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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