BulbSwitcher.js

// Source : https://leetcode.com/problems/bulb-switcher
// Author : Dean Shi
// Date   : 2017-09-05

/***************************************************************************************
 *
 * 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 ith round, you toggle every i
 * bulb. For the nth round, you only toggle the last bulb.
 *
 * Find how many bulbs are on after n rounds.
 *
 * Example:
 *
 * Given n = 3.
 * 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.
 *
 *
 ***************************************************************************************/

/**
 * @param {number} n
 * @return {number}
 */
var bulbSwitch = function(n) {
    return ~~Math.sqrt(n)
};