Binary Search Tree 2

{Searches a binary search tree in O(logn) }

type tree = ^ node;
node = record
left, right : tree;
info : char
end;




function subtree( item : char ) : tree;
{creates a subtree}
var t : tree;
begin
new( t );
t^.info := item;
t^.left := nil;
t^.right := nil;
subtree := t
end;

procedure infix( t : tree);
begin
if t <> nil then begin
infix( t^.left );
write( t^.info );
infix( t^.right )
end
end;


procedure prefix( t : tree);
begin
if t <> nil then begin
write( t^.info );
prefix( t^.left );
prefix( t^.right )
end
end;

procedure postfix( t : tree);
begin
if t <> nil then begin
postfix( t^.left );
postfix( t^.right );
write( t^.info );
end
end;

procedure insert( item : char; var t : tree );
begin
if t = nil then
t := subtree( item )
else if item <= t^.info then insert( item, t^.left) else insert( item, t^.right) end; procedure bst( var root : tree ); {produces a binary search tree} var item : char; begin writeln('type your sentence'); root := nil; while not eoln do begin read( item ); insert( item, root ) end end; procedure search( key: char; var found: boolean; t : tree); begin if (t <> nil) and not found then begin
if key = t^.info then
found := true
else if key < t^.info then
search(key, found, t^.left)
else
search(key, found, t^.right)
end
end;

var root : tree;
found : boolean;
key : char;

begin
bst( root );
infix( root );
writeln;
readln;
writeln( 'type your letter');
found := false;
readln( key );
search( key, found, root);
if found then
writeln( key, ' was found.')
else
writeln( key, ' was not found.');
readln;
readln

end.