langs a-z

Task/Balanced-brackets/XPL0/balanced-brackets.xpl0

@@ -0,0 +1,26 @@
+include c:\cxpl\codes;       \intrinsic code declarations
+
+int     N, I, C, Nest;
+char    Str;
+[\Generate a string with N open brackets and N close brackets in arbitrary order
+N:= IntIn(0);                           \get number of brackets/2 from keyboard
+Str:= Reserve(2*N);
+for I:= 0 to 2*N-1 do Str(I):= ^[;
+C:= 0;                                  \initialize count of "]"
+repeat  I:= Ran(2*N);                   \change N random locations to "]"
+        if Str(I) # ^] then [Str(I):= ^]; C:= C+1];
+until   C>=N;
+
+\Determine whether string consists of nested pairs of open/close brackets
+I:= 0;  C:= 0;  Nest:= false;
+while I<2*N do
+        [if Str(I) = ^[ then C:= C+1 else C:= C-1;
+        if C<0 then Nest:= true;
+        ChOut(0,Str(I));
+        I:= I+1;
+        ];
+ChOut(0,9\tab\);
+if Nest then Text(0,"NOT ");
+Text(0,"OK
+");
+]