state <- as.character(1:9)winner <- FALSEtriples <- list(  c(1,2,3),  c(4,5,6),  c(7,8,9),  c(1,4,7),  c(2,5,8),  c(3,6,9),  c(1,5,9),  c(3,5,7))display<- function(state){  cat(" ", state1, "|", state2, "|", state3,"")  cat(" ---+---+---", "")  cat(" ", state4, "|", state5, "|", state6,"")  cat(" ---+---+---", "")  cat(" ", state7, "|", state8, "|", state9,"")}display(state)update<-function(state, who, pos){  if(who==1)    {statepos<-"X"}  else if(who==2)    {statepos<-"O"}  return(state)}play <- function(){  number_player<-readline("Type '1' to play against computer, Type '2' to play against player ")    if(number_player==1){    who<-readline("Type '1' to play first or Type '2' to play second ")    if(who == 1){      cat("Player Starts First !","")    }    else if(who == 2){      cat("Computer Starts First !","")    }    display(state)    against_computer(state,who)  }    else if(number_player==2){    who<-1;cat("Player 1 Starts First !","")    display(state)    against_human(state,who)  }  else if(number_player !=1 && number_player !=2 ){    cat("Please type either 1 or 2")    play()  }}check_winner<-function(state){    for(i in 1:8){    if(sum(triplesi %in% which(state=="X")) >=3){      cat(“Player X wins”,””)      winner = TRUE      break    }    if(sum(triplesi %in% which(state==”O”)) >=3){      cat(“Player Y wins”,””)      winner = TRUE      break    }  }  if(length(which(state==”X”))+length(which(state==”O”)) == 9 && winner==FALSE){        cat(“DRAW”, “”)    winner=TRUE    } ## Check whether there are any empty position and still no winner  return(winner)}restriction<-function(state){  restrict<-TRUE  while(restrict){    pos<-as.double(readline("Which position would you like to play? (Type a number from 1 to 9) :"))    if((pos>=1 && pos<=9) != TRUE){      cat("Please type a number from 1 to 9","")    }    else{      if(statepos == "X" || statepos == "O"){        cat("Position is already occupied, please type the number with unoccupied position","")              }else if(statepos != "X" && statepos != "O"){        state<-update(state,pos)        restrict=FALSE      }    }  }  return(pos)}against_human<-function(state,who){  while(winner == FALSE){    pos<-restriction(state)    if(who==1){                             state<-update(state, who, pos)       display(state)       winner<-check_winner(state)       who<-2     }    else if(who==2){                        state<-update(state, who, pos)       display(state)      winner<-check_winner(state)       who<-1    }  }}against_computer<-function(state,who){  while(winner == FALSE){    if(who==1){      pos<-restriction(state)      state<-update(state, who, pos)      display(state)      winner<-check_winner(state)      if(winner)        break      state<-computer_turn(state)      cat("Computer makes this move: ", "")      display(state)      cat("Computer has taken the position",which(state=="O"), "")      winner<-check_winner(state)      if(winner)        break      }    else if(who==2){      state<-computer_turn(state)      cat("Computer makes this move: ", "")      display(state)      cat("Computer has taken the position",which(state=="X"), "")      winner<-check_winner(state)      if(winner)        break      pos<-restriction(state)      state<-update(state, who, pos)      display(state)      winner<-check_winner(state)      if(winner)        break    }  }}computer_turn<-function(state){  finding_decider<-function(){    for(i in 1:8){      remainder =statetriplesiwhich((triplesi) %in% which(state=="X")== FALSE)      which(remainder %in% as.character(1:9))        }  }  if(sum(state=="X") > sum(state==”O”)){#human goes first playing x and computer second playing o    before<-state    for(i in 1:8){      if(sum(triplesi %in% which(state=="X"))==2 &&          any(statetriplesiwhich((triplesi %in% which(state=="O"))==FALSE) %in% as.character(1:9)) &&          any(statetriplesiwhich((triplesi %in% which(state=="X"))==FALSE) %in% as.character(1:9))){ #winning        statetriplesiwhich((triplesi %in% which(state=="O"))==FALSE)<-"O"      }      if(identical(state,before)==FALSE)break    }    if(identical(state,before)==TRUE){      for(i in 1:length(triples)){        if(sum(triplesi %in% which(state=="X"))==2 &&            any(statetriplesiwhich((triplesi %in% which(state=="X"))==FALSE) %in% as.character(1:9))&&            any(statetriplesiwhich((triplesi %in% which(state=="O"))==FALSE) %in% as.character(1:9))){#blocking          statetriplesiwhich((triplesi %in% which(state=="X"))==FALSE)<-"O"        }        if(identical(state,before)==FALSE)break      }    }    if(identical(state,before)==TRUE){statesample(which(state == as.character(1:9)),1)<-"O"}  }else if(sum(state=="O") >= sum(state==”X”) || sum(state==”O”)==0){#computer goes first playing x and human second playing o    before<-state    for(i in 1:length(triples)){      if(sum(triplesi %in% which(state=="X"))==2 &&         any(statetriplesiwhich((triplesi %in% which(state=="X"))==FALSE) %in% as.character(1:9))&&          any(statetriplesiwhich((triplesi %in% which(state=="O"))==FALSE) %in% as.character(1:9))){#winning        statetriplesiwhich((triplesi %in% which(state=="X"))==FALSE)<-"X"      }      if(identical(state,before)==FALSE)        break    }            if(identical(state,before)==TRUE){      for(i in 1:length(triples)){        if(sum(triplesi %in% which(state=="O"))==2 &&            any(statetriplesiwhich((triplesi %in% which(state=="O"))==FALSE) %in% as.character(1:9))&&            any(statetriplesiwhich((triplesi %in% which(state=="X"))==FALSE) %in% as.character(1:9))){#blocking          statetriplesiwhich((triplesi %in% which(state=="O"))==FALSE)<-"X"        }        if(identical(state,before)==FALSE)          break      }    }    if(identical(state,before)==TRUE){statesample(which(state == as.character(1:9)),1)<-"X"}  }  return(state)} play()