My fastest "not Math" solution n=10,000,000 t=1071ms

```
public int bulbSwitch(int n) {
if(n<2){
return n;
}
int result = 0;
boolean[] bulbs = new boolean[n+1];
bulbs[1]=true;
for(int swch = 2; swch<=n/2; swch++){
for(int bulb = 2*swch; bulb<n+1; bulb+=swch){
bulbs[bulb] = !bulbs[bulb];
}
}
for(int i = 1; i<=n; i++){
if(bulbs[i]){
result++;
}
}
return result;
}
```