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//
// "Trunks and tails
// Are handy things"
// from Holding Hands
// by Lenore M. Link
//
// Now that we have tails all figured out, can you implement trunks?
//
const std = @import("std");
const Elephant = struct {
letter: u8,
tail: ?*Elephant = null,
trunk: ?*Elephant = null,
visited: bool = false,
// Elephant tail methods!
pub fn getTail(self: *Elephant) *Elephant {
return self.tail.?; // Remember, this means "orelse unreachable"
}
pub fn hasTail(self: *Elephant) bool {
return (self.tail != null);
}
// Your Elephant trunk methods go here!
// ---------------------------------------------------
???
// ---------------------------------------------------
pub fn visit(self: *Elephant) void {
self.visited = true;
}
pub fn print(self: *Elephant) void {
// Prints elephant letter and [v]isited
var v: u8 = if (self.visited) 'v' else ' ';
std.debug.print("{u}{u} ", .{ self.letter, v });
}
};
pub fn main() void {
var elephantA = Elephant{ .letter = 'A' };
var elephantB = Elephant{ .letter = 'B' };
var elephantC = Elephant{ .letter = 'C' };
// We link the elephants so that each tail "points" to the next.
elephantA.tail = &elephantB;
elephantB.tail = &elephantC;
// And link the elephants so that each trunk "points" to the previous.
elephantB.trunk = &elephantA;
elephantC.trunk = &elephantB;
visitElephants(&elephantA);
std.debug.print("\n", .{});
}
// This function visits all elephants twice, tails to trunks.
fn visitElephants(first_elephant: *Elephant) void {
var e = first_elephant;
// We follow the tails!
while (true) {
e.print();
e.visit();
// This gets the next elephant or stops.
if (e.hasTail()) {
e = e.getTail();
} else {
break;
}
}
// We follow the trunks!
while (true) {
e.print();
// This gets the previous elephant or stops.
if (e.hasTrunk()) {
e = e.getTrunk();
} else {
break;
}
}
}
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