How do you solve Print in Order on LeetCode?

Print in Order (LeetCode #1114) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: Understanding thread synchronization is crucial in concurrent programming.

What is the time complexity of Print in Order?

The optimal solution for Print in Order runs in O(n) time and uses O(1) space. The complexity is O(n) because each thread executes in a linear sequence without any nested waiting or checks.

What is the brute force solution for Print in Order?

The brute force approach for Print in Order is Brute Force, with O(n²) time complexity and O(1) space complexity. In the brute-force approach, we can use simple synchronization techniques to control the order of execution of the threads. We can use flags or simple wait-notify mechanisms to ensure that each thread waits for the previous one to complete. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Print in Order?

Print in Order uses the following concepts: Concurrency. The recommended patterns to study are: Semaphore, Condition Variable.

What are the interview tips for Print in Order?

Always clarify the requirements regarding thread execution order. Discuss potential edge cases, such as thread starvation or deadlocks. Practice explaining your thought process clearly while coding.

What are common mistakes when solving Print in Order?

Not properly managing thread states, leading to deadlocks. Using busy waiting instead of proper synchronization mechanisms.

#1114

Print in Order

Easy

ConcurrencySemaphoreCondition Variable

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(1)

💡

Intuition

Time O(n)Space O(1)

In the optimal solution, we can use a more structured approach with semaphores or condition variables to manage the order of execution without busy waiting. This allows threads to efficiently wait for the appropriate signal to proceed.

⚙️

Algorithm

4 steps

1Step 1: Initialize three semaphores for first, second, and third with initial values set to control the order.
2Step 2: In the first() method, signal the second semaphore after printing.
3Step 3: In the second() method, wait on the first semaphore and signal the third semaphore after printing.
4Step 4: In the third() method, wait on the second semaphore and print.

solution.py19 lines

1import threading
2
3class Foo:
4    def __init__(self):
5        self.sema1 = threading.Semaphore(0)
6        self.sema2 = threading.Semaphore(0)
7
8    def first(self):
9        print('first')
10        self.sema1.release()
11
12    def second(self):
13        self.sema1.acquire()
14        print('second')
15        self.sema2.release()
16
17    def third(self):
18        self.sema2.acquire()
19        print('third')

ℹ

Complexity note: The complexity is O(n) because each thread executes in a linear sequence without any nested waiting or checks.

1Understanding thread synchronization is crucial in concurrent programming.
2Using semaphores or condition variables can greatly simplify thread coordination.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.