Leetcode #1115: Print FooBar Alternately
In this guide, we solve Leetcode #1115 Print FooBar Alternately in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Suppose you are given the following code: class FooBar { public void foo() { for (int i = 0; i < n; i++) { print("foo"); } } public void bar() { for (int i = 0; i < n; i++) { print("bar"); } } } The same instance of FooBar will be passed to two different threads: thread A will call foo(), while thread B will call bar(). Modify the given program to output "foobar" n times.
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: Concurrency
Intuition
The constraints allow a direct scan that keeps only the essential state.
By translating the requirements into a clean loop, the logic stays easy to reason about.
Approach
Iterate through the data once, updating the state needed to compute the answer.
Return the final state after the traversal is complete.
Steps:
- Parse the input.
- Iterate and update state.
- Return the computed answer.
Example
class FooBar {
public void foo() {
for (int i = 0; i < n; i++) {
print("foo");
}
}
public void bar() {
for (int i = 0; i < n; i++) {
print("bar");
}
}
}
Python Solution
from threading import Semaphore
class FooBar:
def __init__(self, n):
self.n = n
self.f = Semaphore(1)
self.b = Semaphore(0)
def foo(self, printFoo: "Callable[[], None]") -> None:
for _ in range(self.n):
self.f.acquire()
# printFoo() outputs "foo". Do not change or remove this line.
printFoo()
self.b.release()
def bar(self, printBar: "Callable[[], None]") -> None:
for _ in range(self.n):
self.b.acquire()
# printBar() outputs "bar". Do not change or remove this line.
printBar()
self.f.release()
Complexity
The time complexity is , and the space complexity is . The space complexity is .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.