A group of three students, that is to say, you don't have to look at his numbers, just look at the number of times you pull the lamp, which are 1 time, 2 times and 3 times respectively.

A cycle * * * pulls 6 times * *100 students, each group has three people ***33 groups with one more person 6*33, and the complete cycle is the one that pulls 198 times.

If 100 is divided by more than 3, it belongs to "3K+ 1, and the switch is turned on once", 198+ 1, * * * and the switch is turned on once.

There are four situations, which are regular cycles. Divide 199 by four situations, and there are 49 cycles, and there are three pulls, that is, all three lights are on.