day 6, AWK solution

d06/exec.awk

@@ -0,0 +1,17 @@
+BEGIN { W = 14 }
+{
+	for (i=1; i<=length($1); i++) {
+		window = substr($1,i,W)
+		# compare each char of window to all char of window
+		S = 0  # to count match
+		for (j=1; j<=W; j++) {
+			for (k=j; k<=W; k++) {
+				S+= (substr(window,j,1) == substr(window,k,1)) ? 1 : 0
+			}
+		}
+		if (S == W) {  # if each char match only with itsef
+			print i + W - 1
+			next  # finish
+		}
+	}
+}