{ "data": { "question": { "questionId": "319", "questionFrontendId": "319", "boundTopicId": null, "title": "Bulb Switcher", "titleSlug": "bulb-switcher", "content": "

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

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On the third round, you toggle every third bulb (turning on if it's off or turning off if it's on). For the ith round, you toggle every i bulb. For the nth round, you only toggle the last bulb.

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Return the number of bulbs that are on after n rounds.

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Example 1:

\n\"\"\n
\nInput: n = 3\nOutput: 1\nExplanation: At first, the three bulbs are [off, off, off].\nAfter the first round, the three bulbs are [on, on, on].\nAfter the second round, the three bulbs are [on, off, on].\nAfter the third round, the three bulbs are [on, off, off]. \nSo you should return 1 because there is only one bulb is on.
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Example 2:

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\nInput: n = 0\nOutput: 0\n
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Example 3:

\n\n
\nInput: n = 1\nOutput: 1\n
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\n

Constraints:

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Compiled with clang 11 using the latest C++ 20 standard.

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Your code is compiled with level two optimization (-O2). AddressSanitizer is also enabled to help detect out-of-bounds and use-after-free bugs.

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Most standard library headers are already included automatically for your convenience.

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OpenJDK 17. Java 8 features such as lambda expressions and stream API can be used.

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Most standard library headers are already included automatically for your convenience.

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Python 2.7.12.

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C# 10 with .NET 6 runtime

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Node.js 16.13.2.

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