The minimum state DFA which accepts all the binary strings with number of 1’s divisible by 3 requires
1 state for determination is number of input elements equal 1 is divisible by 3. If this number really is divisible by 3 then state preserves, else we move to second state. In second state we again analyze number of input 1, and we move to state 1, if this number becomes divisible by 3.
Result will be state of our DFA: if final state is 1, then input string had 3n elements 1, else it will be state 2.