125_ Fsm3onehot.v

module top_module(
    input in,
    input [3:0] state,
    output [3:0] next_state,
    output out); //

    parameter A=0, B=1, C=2, D=3;

    // State transition logic: Derive an equation for each state flip-flop.
    assign next_state[A] = state[A] & (~in) | state[C] & (~in);
    assign next_state[B] = state[A] & in | state[B] & in | state[D] & in;
    assign next_state[C] = state[B] & (~in) | state[D] & (~in);
    assign next_state[D] = state[C] & (in);

    // Output logic: 
    assign out = (state[D] == 1);

endmodule