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This approach employs semaphores to control the execution order of methods. Since semaphores are synchronization constructs that can be used to control access to a common resource in a concurrent system, we can use them to gate the execution of 'second' and 'third' methods until 'first' and 'second' have completed, respectively. The semaphore for 'second' starts at 0 and is incremented by 'first', allowing 'second' to run. Similarly, 'third' can proceed only after 'second' increments its semaphore.
Time Complexity: O(1) for each method call. Space Complexity: O(1).
1from threading import Semaphore
2
3class Foo:
4 def __init__(self):
5 self.second_semaphore = Semaphore(0)
6 self.third_semaphore = Semaphore(0)
7
8 def first(self, printFirst: 'Callable[[], None]') -> None:
9 printFirst()
10 self.second_semaphore.release()
11
12 def second(self, printSecond: 'Callable[[], None]') -> None:
13 self.second_semaphore.acquire()
14 printSecond()
15 self.third_semaphore.release()
16
17 def third(self, printThird: 'Callable[[], None]') -> None:
18 self.third_semaphore.acquire()
19 printThird()In Python, we utilize the Semaphore class from the threading module. We initiate two semaphores, each initialized to 0. The first method prints 'first' and then releases the semaphore for second. The second method waits (acquires) on the semaphore before printing 'second' and then releases the semaphore for third. The third method waits (acquires) on its semaphore before printing 'third'.
This approach leverages locks and condition variables to achieve the desired execution order. By associating each method with a condition variable, the appropriate method waits (and releases lock) until the previous condition is signaled, facilitating the required sequence.
Time Complexity: O(1) for each method call. Space Complexity: O(1).
1class Foo {
2 constructor() {
3
In JavaScript, since there's no native semaphore or lock, we utilize promises for sequencing - each method holds a promise chain, ensuring the sequence is maintained. Each call ensures that the previous methods have completed execution before proceeding.