!c29_1_5snakes_ladders.f95
integer function next_state(i,trans,n)
real::trans(n,n),cum_prob(n),r
integer::mnloc(1)
!  the random next_state after i
endfunction

program snakes_ladders_individual
real::trans(9,9)=0,average=0
integer,parameter::inf=10**5
integer::n,next_state,nummoves,history(200)
! 1, 2, ..., 9 = board positions,  trans = transition probabilities
trans(1,7)=.5; trans(1,5)=.5
trans(2,5)=.5; trans(2,4)=.5
trans(3,4)=.5; trans(3,5)=.5
trans(4,5)=.5; trans(4,1)=.5
trans(5,1)=.5; trans(5,7)=.5
trans(7,4)=.5; trans(7,9)=.5
trans(8,9)=.5; trans(8,9)=.5
do n=1,inf
  !play game
  history=0;i=1;history(1)=1
  do k=2,200
     i=next_state(i,trans,9)
     history(k)=i; if(i==9) exit
  enddo
  !update records and print play
  nummoves=count(history/=0)-1
  average=(average*(n-1)+real(nummoves))/n
  if(mod(n,6000)/=1)cycle
  print 11,nummoves,history(1:nummoves+1)
enddo
11 format(i3," moves",200(i3))
print '(a,f5.3,/)', "Average number of moves is ",average
endprogram