$ cat spw759180_NetWallah 
#!/usr/bin/perl
#
use strict;
use warnings;

my @probs =(0,0.1,0.53,0.51,0.59,0.67,0.2,0.04,0.05,0.56,0.89,0.75,0.6);
my $t;
print $_ . (",","\n")[$t=1-$t]  
    for  grep {($probs[$_] >=.5 .. $probs[$_]> .5) and $t=!$t }
           0..$#probs
$ ./spw759180_NetWallah
2
4,9
11,$