Leetcode 319

This is a harder question for me, write on paper and find the parttern.

class Solution {
    public int bulbSwitch(int n) {
        // n == 0 all bulbs are off
        // n == 1 all bulbs with factor of 1 
        // n == 2 all bulbs with factor 2 (2,4,6,8,10)...
        // n == 3 all bulbs with factor 3 (3,6,9).....
        // ......
        // so we are finding number from 1 to n are perfect square
        // essencially we are trying to find the sqrt of the n 
        return (int) Math.sqrt(n);
    }
}