tcl: sorting list depending on array - list

Question

If List1 is:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
And array1 is:
{3 4 5} {12 13} {20 21}
How do I convert list1 according to array1 by replacing reverse list of each element of array1, i.e., producing this
output:
1 2 5 4 3 6 7 8 9 10 11 13 12 14 15 16 17 18 19 21 20 22 23 24 25
^^^^^ ^^^^^ ^^^^^

Answer 1

This is not a sorting task, this is a searching task.
If you assume that the ranges to reverse do not overlap, but are not necessarily present either (i.e., not using the fact that they are contiguous numbers), you get something like this:
# Iterate over each of the replacement patterns
foreach range $array1 {
# Iterate over each of the locations where the first element of the current
# replacement pattern is found
foreach pos [lsearch -all -exact $list1 [lindex $range 0]] {
# This will be the index of the *last* element in each subrange
set pos2 [expr {$pos + [llength $range] - 1}]
# Do the reversed replacement if the ranges match
if {[lrange $list1 $pos $pos2] eq $range} {
set list1 [lreplace $list1 $pos $pos2 {*}[lreverse $range]]
}
}
}
The result after this will be in the updated list1 variable. Wrapping into a procedure is left as an exercise.