_319.java

package com.fishercoder.solutions;

/**
 * 319. 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 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.
 */
public class _319 {

    public int bulbSwitch(int n) {
        if (n < 2) {
            return n;
        }
        return (int) Math.sqrt(n);
    }

}