day 15 stats, thanks alderwick!

15/15.awk

@@ -0,0 +1,32 @@
+# algorithm proposed by alderwick :)
+BEGIN{ FS = "" }
+
+function p(x,y){ return x","y }
+
+{ for(i=1;i<=NF;i++) r[p(i,NR)] = $i }
+
+END{
+	s[p(1,1)] = 0
+	target = 1
+	while(!(p(NF,NR) in s)){
+		print "target:",target
+		delete ns
+		for(i in s){
+			split(i,arr,",")
+			x = arr[1]; y=arr[2]
+			cs = s[p(x,y)]
+			if(cs<target-9) continue # too far from target score
+			if(x>1 && r[p(x-1,y)]+cs==target && s[p(x-1,y)]=="" )
+				ns[p(x-1,y)] = target # left
+			if(x<NF && r[p(x+1,y)]+cs==target && s[p(x+1,y)]=="" )
+				ns[p(x+1,y)] = target  #right
+			if(y>1 && r[p(x,y-1)]+cs==target && s[p(x,y-1)]=="" )
+				ns[p(x,y-1)] = target # up
+			if(y<NR && r[p(x,y+1)]+cs==target && s[p(x,y+1)]=="" )
+				ns[p(x,y+1)] = target # down
+		}
+		for(i in ns) s[i] = ns[i]
+		target++
+	}
+	print s[p(NF,NR)]
+}

15/15_2.awk

@@ -0,0 +1,37 @@
+# algorithm proposed by alderwick :)
+BEGIN{ FS = "" }
+
+function p(x,y){ return x","y }
+
+function risk(x,y){
+	x--; y--; # zero based
+	return (r[p(x%NF+1,y%NF+1)] + int(x/NF) + int(y/NR)-1)%9 + 1
+}
+
+{ for(i=1;i<=NF;i++) r[p(i,NR)] = $i }
+
+END{
+	s[p(1,1)] = 0
+	target = 1
+	while(!(p(NF*5,NR*5) in s)){
+		if(target%100==0) print "target:",target
+		delete ns
+		for(i in s){
+			split(i,arr,",")
+			x = arr[1]; y=arr[2]
+			cs = s[p(x,y)]
+			if(cs<target-9) continue # too far from target score
+			if(x>1 && risk(x-1,y)+cs==target && s[p(x-1,y)]=="" )
+				ns[p(x-1,y)] = target # left
+			if(x<NF*5 && risk(x+1,y)+cs==target && s[p(x+1,y)]=="" )
+				ns[p(x+1,y)] = target  #right
+			if(y>1 && risk(x,y-1)+cs==target && s[p(x,y-1)]=="" )
+				ns[p(x,y-1)] = target # up
+			if(y<NR*5 && risk(x,y+1)+cs==target && s[p(x,y+1)]=="" )
+				ns[p(x,y+1)] = target # down
+		}
+		for(i in ns) s[i] = ns[i]
+		target++
+	}
+	print s[p(NF*5,NR*5)]
+}

15/Makefile

@@ -0,0 +1,14 @@
+1t:
+	awk -f 15.awk test
+
+1i:
+	awk  -f 15.awk input
+
+2t:
+	awk  -f 15_2.awk test
+
+2i:
+	awk  -f 15_2.awk input
+
+paste:
+	xclip -sel c -o > test

README.md

@@ -27,6 +27,7 @@ awk -c -f 01.awk inputfile
 ```
       -------Part 1--------   -------Part 2--------
 Day       Time  Rank  Score       Time  Rank  Score
+ 15   16:52:00  24420     0   17:30:02  20656     0 --- thanks alderwick for your help!
  14   00:27:53  4878      0   01:07:47  3311      0
  13   02:02:33  9507      0   02:19:53  9225      0 --- started late
  12   01:57:59  7241      0   02:16:49  6447      0