Bulb Switcher — LeetCode 319 Python Solution

The problem

There are n bulbs that are initially off. You first turn on all the bulbs, then you turn off every second bulb.

Example

Input

n = 3

Output

1

Explanation

At first, the three bulbs are [off, off, off].

Python solution

class Solution:
    def bulbSwitch(self, n: int) -> int:
        return int(sqrt(n))

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 319. Bulb Switcher is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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