day 2, double awk

d02/combine.awk

@@ -0,0 +1,14 @@
+# emit a report and its variants as a bloc, separated by empty line
+{
+  print
+  for (i=1;i<=NF;i++) {
+    r = ""
+    for (j=1;j<=NF;j++) {
+      if (i!=j) {
+        r = r $j " "
+      }
+    }
+    print r
+  }
+  print ""
+}

d02/part1.awk

@@ -0,0 +1,17 @@
+{
+  p = ($2 -$1) < 0 ? -1 : 1
+  safe = 1
+  for (i=2;i<=NF;i++) {
+    d = ($i - $(i-1))
+    q = d < 0 ? -1 : 1
+    if (p != q || d>3 || d<-3 || d == 0) {
+      safe = 0
+      break
+    } 
+  }
+  #print NR, $0 , p, safe
+  S += safe
+}
+END {
+  print S
+}

d02/part2.awk

@@ -0,0 +1,25 @@
+# run with awk -f combine.awk < input | awk -f part2.awk 
+length == 0 {
+  #print "onesafe", onesafe
+  S+= onesafe>0  # if at least one variant is safe, then report is safe
+  onesafe = 0
+  next
+}
+{
+  p = ($2 -$1) < 0 ? -1 : 1  # uphill or downhill
+  safe = 1
+  for (i=2;i<=NF;i++) {
+    d = ($i - $(i-1))
+    q = d < 0 ? -1 : 1
+    if (q != p || d>3 || d<-3 || d == 0) {
+      safe = 0
+      break
+    } 
+  }
+  #print NR, $0 , p, safe
+  onesafe += safe
+}
+
+END {
+  print S
+}