From e8849566baf01424909f797d9db7db36e432b0c2 Mon Sep 17 00:00:00 2001
From: Marc Durdin <marc@durdin.net>
Date: Tue, 4 Jan 2022 12:35:51 +1100
Subject: [PATCH] fix(amazing): guarantee exit on bottom row of maze

This issue only tends to show up on very small mazes (e.g. 2x2, 3x3). It is possible for the algorithm to never generate an exit to the maze. While the algorithm guarantees with the `Z` variable that only one exit will be generated, it does not test for the situation where we just happen to never get the right random value to open an exit on the bottom row.

The simplest resolution is just to check for this before rendering the final result (i.e. `IF Z=0`), and add an exit to a random cell on the bottom row.
---
 02_Amazing/amazing.bas | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/02_Amazing/amazing.bas b/02_Amazing/amazing.bas
index 63255319..3b39c93a 100644
--- a/02_Amazing/amazing.bas
+++ b/02_Amazing/amazing.bas
@@ -117,10 +117,15 @@
 975 V(R,S)=3:Q=0:GOTO 1000
 980 V(R,S)=1:Q=0:R=1:S=1:GOTO 250
 1000 GOTO 210
-1010 FOR J=1 TO V
-1011 PRINT "I";
-1012 FOR I=1 TO H
-1013 IF V(I,J)<2 THEN 1030
+1010 IF Z=1 THEN 1015
+1011 X=INT(RND(1)*H+1)
+1012 IF V(X,V)=0 THEN 1014
+1013 V(X,V)=3: GOTO 1015
+1014 V(X,V)=1
+1015 FOR J=1 TO V
+1016 PRINT "I";
+1017 FOR I=1 TO H
+1018 IF V(I,J)<2 THEN 1030
 1020 PRINT "   ";
 1021 GOTO 1040
 1030 PRINT "  I";