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  • 319. Bulb Switcher

    package LeetCode_319
    
    /**
     * 319. Bulb Switcher
     * https://leetcode.com/problems/bulb-switcher/
     *
     * There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb.
     * On the third round, you toggle every third bulb (turning on if it's off or turning off if it's on).
     * For the i-th round, you toggle every i bulb. For the n-th round, you only toggle the last bulb.
     * Find how many bulbs are on after n rounds.
     *
    Example:
    Input: 3
    Output: 1
    Explanation:
    At first, the three bulbs are [off, off, off].
    After first round, the three bulbs are [on, on, on].
    After second round, the three bulbs are [on, off, on].
    After third round, the three bulbs are [on, off, off].
    So you should return 1, because there is only one bulb is on.
     * */
    class Solution {
        /*
        * solution: Math, Time complexity:O(sqrt(n)), Space complexity:O(1)
        * init:    X    X    X    X    X
          first:      √    √    √    √    √
          second:      √     X    √    X    √
          third:      √     X    X    X    √
          fourth:      √     X    X    √    √
          fifth:      √     X    X    √    X
           all squared bulbs will be lit
        * */
        fun bulbSwitch(n: Int): Int {
            var result = 1
            while (result * result <= n) {
                result++
            }
            return result - 1
        }
    }
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  • 原文地址:https://www.cnblogs.com/johnnyzhao/p/13936974.html
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