A Simplistic TCP Finite State Machine (FSM)

• Time : $O(|events|log(|events|))$
• Space : $O(1)$

#include <string>
#include <vector>

using namespace std;
map<pair<string, string>, string> adj;
std::string traverse_TCP_states(const std::vector<std::string> &events){
    adj[{"CLOSED","APP_PASSIVE_OPEN"}] = "LISTEN";
    adj[{"CLOSED","APP_ACTIVE_OPEN"}] = "SYN_SENT";
    adj[{"LISTEN","RCV_SYN"}] = "SYN_RCVD";
    adj[{"LISTEN","APP_SEND"}] = "SYN_SENT";
    adj[{"LISTEN","APP_CLOSE"}] = "CLOSED";
    adj[{"SYN_RCVD","APP_CLOSE"}] = "FIN_WAIT_1";
    adj[{"SYN_RCVD","RCV_ACK"}] = "ESTABLISHED";
    adj[{"SYN_SENT","RCV_SYN"}] = "SYN_RCVD";
    adj[{"SYN_SENT","RCV_SYN_ACK"}] = "ESTABLISHED";
    adj[{"SYN_SENT","APP_CLOSE"}] = "CLOSED";
    adj[{"ESTABLISHED","APP_CLOSE"}] = "FIN_WAIT_1";
    adj[{"ESTABLISHED","RCV_FIN"}] = "CLOSE_WAIT";
    adj[{"FIN_WAIT_1","RCV_FIN"}] = "CLOSING";
    adj[{"FIN_WAIT_1","RCV_FIN_ACK"}] = "TIME_WAIT";
    adj[{"FIN_WAIT_1","RCV_ACK"}] = "FIN_WAIT_2";
    adj[{"CLOSING","RCV_ACK"}] = "TIME_WAIT";
    adj[{"FIN_WAIT_2","RCV_FIN"}] = "TIME_WAIT";
    adj[{"TIME_WAIT","APP_TIMEOUT"}] = "CLOSED";
    adj[{"CLOSE_WAIT","APP_CLOSE"}] = "LAST_ACK";
    adj[{"LAST_ACK","RCV_ACK"}] = "CLOSED";
    string state = "CLOSED";
    for(auto e : events) {
        if(adj.count({state, e})) state = adj[{state,e}];
        else return "ERROR";
    }
    return state;
}