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