day 9 part 2

09/2.tcl

@@ -0,0 +1,94 @@
+set fp [open "input"]
+gets $fp line
+close $fp
+
+set line_len [string length $line]
+set layout {}
+set is_file 1
+set file_no 0
+for {set i 0} {$i < $line_len} {incr i} {
+    set num [string index $line $i]
+    if {$is_file} {
+        for {set j 0} {$j < $num} {incr j} {
+            lappend layout $file_no
+        }
+        incr file_no
+    } else {
+        for {set j 0} {$j < $num} {incr j} {
+            lappend layout -1
+        }
+    }
+    set is_file [expr {! $is_file}]
+}
+
+proc swap {lst lstart rstart len} {
+    upvar $lst uplst
+    set lend [expr {$lstart + $len - 1}]
+    set rend [expr {$rstart + $len - 1}]
+    set t [lrange $uplst $rstart $rend]
+    set uplst [lreplace $uplst $rstart $rend {*}[lrange $uplst $lstart $lend]]
+    set uplst [lreplace $uplst $lstart $lend {*}$t]
+}
+
+proc skip_space {layout rp} {
+    while {[lindex $layout $rp] == -1 && $rp >= 0} {
+        incr rp -1
+    }
+    return $rp
+}
+
+proc find_next_file {layout rp} {
+    set c [lindex $layout $rp]
+    while {$rp >= 0 && [lindex $layout $rp] == $c} {
+        incr rp -1
+    }
+    incr rp
+    return $rp
+}
+
+proc find_space {layout len end} {
+    set size 0
+    for {set i 0} {$i < $end} {incr i} {
+        set x [lindex $layout $i]
+        if {$x == -1} {
+            incr size
+        }
+        if {$size == $len} {
+            return [expr {$i - $len + 1}]
+        }
+        if {$x != -1} {
+            set size 0
+        }
+    }
+    return -1
+}
+
+set rp [expr {[llength $layout] - 1}]
+
+while {$rp >= 0} {
+    set rp [skip_space $layout $rp]
+    if {$rp < 0} { break }
+    set new_rp [find_next_file $layout $rp]
+    set len [expr {$rp - $new_rp + 1}]
+    if {$rp < 0} { break }
+    set lp [find_space $layout $len $new_rp]
+    if {$lp >= 0} {
+        swap layout $lp $new_rp $len
+    }
+    set rp $new_rp
+    incr rp -1
+}
+set checksum 0
+set i 0
+while {1} {
+    if {$i >= [llength $layout]} {
+        break
+    }
+    if {([lindex $layout $i] == -1)} {
+        incr i
+        continue
+    }
+    incr checksum [expr {[lindex $layout $i] * $i}]
+    incr i
+}
+puts $checksum