day 7 part 2

07/2.tcl

@@ -0,0 +1,31 @@
+set fp [open "input"]
+set equations {}
+while {[gets $fp line] >= 0} {
+    set s1 [split $line ":"]
+    lappend equations $s1
+}
+
+proc can_match_impl {target numbers current} {
+    if {0 == [llength $numbers]} {
+        return [expr {$target == $current}]
+    }
+    set rest [lrange $numbers 1 end]
+    set first [lindex $numbers 0]
+    return [expr {[can_match_impl $target $rest [expr {$current * $first}]]
+                    || [can_match_impl $target $rest [expr {$current + $first}]]
+                    || [can_match_impl $target $rest "$current$first"]}]
+}
+
+proc can_match {target numbers} {
+    return [can_match_impl $target [lrange $numbers 1 end] [lindex $numbers 0]]
+}
+
+set sum 0
+foreach elem $equations {
+    set test_value [lindex $elem 0]
+    set numbers [lindex $elem 1]
+    if {[can_match $test_value $numbers]} {
+        set sum [expr {$sum + $test_value}]
+    }
+}
+puts $sum