1 files changed, 47 insertions, 0 deletions
diff --git a/2024/tcl/02.tcl b/2024/tcl/02.tcl
new file mode 100755
index 0000000..dac290e
--- /dev/null
+++ b/2024/tcl/02.tcl
@@ -0,0 +1,47 @@
+#!/bin/env tclsh
+
+source lib.tcl
+setup 2
+
+puts {Part 1: Count "safe" ordered sequences with intervals such that 1 <= x <= 3.}
+
+proc row_errs {row} {
+  set report [lassign $row first second]
+  set neg [expr {abs($second - $first) != ($second - $first)}]
+  set prev $first
+
+  set row_errs 0
+  foreach num [concat $second $report] {
+    if {$neg != (abs($num - $prev) != ($num - $prev)) ||
+        abs($num - $prev) > 3 || abs($num - $prev) < 1} {
+      incr row_errs
+    } else {
+      set prev $num
+    }
+  }
+  return $row_errs
+}
+
+while {[gets $input report] != -1} {
+  if ![row_errs $report] { incr safe_count; continue }
+  # naive, but handles a case like [1 4 2 3] where removing 2 makes it
+  # safe but an iterative approach only trips on [2]. backtracking
+  # might be better but idc
+  for {set i 0} {$i < [llength $report]} {incr i} {
+    if ![row_errs [lreplace $report $i $i]] {
+      incr dampened_safe_count
+      break
+    }
+  }
+}
+
+incr dampened_safe_count $safe_count
+
+close $input
+
+puts "Safe sequence count: $safe_count"
+
+puts ""
+puts {Part 2: Tolerate 1 bad entry in a report.}
+
+puts "Dampened sequence count: $dampened_safe_count"