Solution for 08-01

NOTES.md

@@ -13,6 +13,7 @@ Notes, thoughts, or questions that arose as I implemented the solutions. Hopeful
 * [Continue expressions](https://ziglang.org/documentation/master/#while) - don't need to remember to put the index-incrementing code at the end of every branch!
 * Great powerful `switch` syntax (though not as powerful as Rust's)
 * Labelled loops - _usually_ should be avoided, but helpful on occasion!
+* `defer` - though, unlike in GoLang where it's a nice-to-have that allows one to do cleanup, here it is _absolutely essential_ for all the manual `deinit`s and `free`s
 
 # Things that I've found missing from this language
 
@@ -22,6 +23,7 @@ Hmmmm, right now it seems even worse than GoLang. Though the Error handling is _
 * [String equality](https://nofmal.github.io/zig-with-example/string-handling/#string-equal)
 * Switching on strings
 * [Iterating over values of an enum](https://zig.guide/language-basics/enums) - [this](https://ziggit.dev/t/iterating-over-a-packed-enum/6530) suggests that it's possible, but testing indicates that that only works at comptime.
+* [Sets](https://github.com/ziglang/zig/issues/6919) (though, as the top comment points out, that's not _too_ bad as you can abuse a HashMap for it)
 
 ## Not "missing", but...
 
@@ -198,4 +200,8 @@ fn accumulate() ![]u32 {
     @memcpy(response, list.items);
     return response;
 }
-```
+```
+
+## What's the point in `HashMap.getOrPut`?
+
+`getOrPut` _doesn't_ actually `put` anything, it _only_ `get`s. See https://ziggit.dev/t/whats-the-point-in-hashmap-getorput/7547.

inputs/08/real.txt

@@ -0,0 +1,50 @@
+..............U.............c.....3...............
+.....p.........F..................................
+.....m..7....................4x............3......
+..e.............F..........c...YH..3..............
+.......e...................................c..E..8
+................a...U................8............
+..............................4.F...8....x........
+............7.....4............Hc..E.......x......
+........p..............................E..........
+.............U.e....................x....t........
+.7..........................Z.H....g..............
+.........7..m.....S.........................E.....
+...F.....p...........6...SY.......................
+.................6..k...................g.........
+..........m......a........................g.......
+.......M.......................................g..
+..............a............Y....C........H........
+....u.......6........a.........C.GY...............
+.....M..................S......................2..
+..........M........S.....................2........
+........M.......................5.........z..f....
+.....................................Z........t.2.
+..........6.......................................
+......................................G...........
+.........................A.........G9....Z........
+........................C.........................
+.....k......................G......z..t...........
+.......k......................zs....f........5...9
+................h........................9....2...
+.............h.....0...........f.....K..ZX........
+..................................f...............
+.......1....................9.........Xz..........
+...............1......B.s......X..................
+............h...............B.....................
+..T.........k..................b..................
+...............u..................................
+.........u.............h..................0.......
+..............y...................................
+...............................t....X......5......
+.................A............................5...
+................u..................s..............
+.T..........b....y................................
+............y............................K........
+..1...............................s....B..........
+..............Ay.............B...P................
+..........T.......................K...........0...
+.............T..................P.........K.......
+......A....P......................................
+....b.........1...................................
+.........b................................P.......

inputs/08/test.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............

scratch.zig

@@ -1,25 +1,26 @@
 const std = @import("std");
 const print = std.debug.print;
 
-test "Demo accumulation" {
-    const accumulated = try accumulate();
-    print("DEBUG - accumulated values are {any}\n", .{accumulated});
-}
+const expect = @import("std").testing.expect;
 
-fn accumulate() ![]u32 {
+test "Len of an iterator is not the same as size" {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
     defer _ = gpa.deinit();
     const allocator = gpa.allocator();
 
-    var list = std.ArrayList(u32).init(allocator);
-    defer list.deinit();
-    try list.append(1);
-    try list.append(2);
-    try list.append(3);
+    var map = std.AutoHashMap(u8, u8).init(allocator);
+    try map.put('a', 'b');
+    try map.put('c', 'd');
+    try map.put('e', 'f');
 
-    const response = try allocator.alloc(u32, list.items.len);
-    @memcpy(response, list.items);
-    return response;
+    var keyIterator = map.keyIterator();
+    const length = keyIterator.len;
+    var counted_length: usize = 0;
+    while (keyIterator.next()) |_| {
+        counted_length += 1;
+    }
+    print("DEBUG - length is {} and counted_length is {}\n", .{ length, counted_length });
+    try expect(length == counted_length);
 }
 
 pub fn main() !void {
@@ -42,5 +43,3 @@ pub fn main() !void {
 fn doIt(string: *const [3:0]u8) *const [9:0]u8 {
     return "prefix" ++ string;
 }
-
-const expect = @import("std").testing.expect;

solutions/08.zig

@@ -0,0 +1,134 @@
+const std = @import("std");
+const print = std.debug.print;
+const util = @import("util.zig");
+
+pub fn main() !void {
+    const response = try part_one(false);
+    print("{}\n", .{response});
+}
+
+const Point = struct { x: usize, y: usize };
+
+fn part_one(is_test_case: bool) !usize {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+    const allocator = gpa.allocator();
+
+    const input_file = try util.getInputFile("08", is_test_case);
+    const data = try util.readAllInputWithAllocator(input_file, allocator);
+    defer allocator.free(data);
+    print("DEBUG - created data", .{});
+
+    // In this problem I'm experimenting with not even parsing the input into lines, but just keeping a "line counter"
+    // that is incremented whenever we hit a `\n` character
+    var width: ?usize = null;
+    var height: ?usize = null;
+    var x: usize = 0;
+    var y: usize = 0;
+    var antennae = std.AutoHashMap(u8, std.ArrayList(Point)).init(allocator);
+    defer antennae.deinit();
+
+    for (data) |c| {
+        print("DEBUG - checking {c} at {}, {}\n", .{ c, x, y });
+        switch (c) {
+            '\n' => {
+                if (width == null) {
+                    width = x;
+                }
+                x = 0;
+                y += 1;
+            },
+            '.' => {
+                x += 1;
+            },
+            else => {
+                const point = Point{ .x = x, .y = y };
+                // https://ziggit.dev/t/problem-with-hashmaps/7221 was helpful!
+                var result = try antennae.getOrPut(c);
+                if (!result.found_existing) {
+                    result.value_ptr.* = std.ArrayList(Point).init(allocator);
+                }
+                try result.value_ptr.append(point);
+                x += 1;
+            },
+        }
+    }
+    height = y; // No `+1` because the trailing newline will do that for us.
+    print("DEBUG - height is {} and width is {}\n", .{ height.?, width.? });
+
+    // Zig lacks a Set (https://github.com/ziglang/zig/issues/6919), so we abuse a HashMap to pretend
+    var all_antinodes = std.AutoHashMap(Point, usize).init(allocator);
+    defer all_antinodes.deinit();
+
+    var it = antennae.valueIterator();
+    while (it.next()) |v| {
+        const node_pairs = try pairs(v.items, allocator);
+        defer allocator.free(node_pairs);
+        for (node_pairs) |node_pair| {
+            const antinodes = try findAntinodes(node_pair, width.?, height.?, allocator);
+            defer allocator.free(antinodes);
+            for (antinodes) |antinode| {
+                try all_antinodes.put(antinode, 1); // We don't actually need to put any value - just populating the key
+            }
+        }
+        // allocator.free(v); <-- because we can't do this, there will still always be memory leaked :'(
+    }
+
+    var count: usize = 0;
+    var antinode_iterator = all_antinodes.keyIterator();
+    print("DEBUG - antinodes are:\n", .{});
+    while (antinode_iterator.next()) |antinode| {
+        print("{}\n", .{antinode});
+        count += 1;
+    }
+    return count;
+}
+
+fn pairs(nodes: []Point, allocator: std.mem.Allocator) ![][2]Point {
+    var output = std.ArrayList([2]Point).init(allocator);
+    defer output.deinit();
+    var a: usize = 0;
+    while (a < nodes.len - 1) : (a += 1) {
+        var b = a + 1;
+        while (b < nodes.len) : (b += 1) {
+            try output.append(.{ nodes[a], nodes[b] });
+        }
+    }
+    return output.toOwnedSlice();
+}
+
+fn findAntinodes(nodes: [2]Point, width: usize, height: usize, allocator: std.mem.Allocator) ![]Point {
+    var response = std.ArrayList(Point).init(allocator);
+    defer response.deinit();
+
+    if (2 * nodes[1].x >= nodes[0].x and 2 * nodes[1].y >= nodes[0].y) {
+        const antiNode1 = Point{ .x = 2 * nodes[1].x - nodes[0].x, .y = 2 * nodes[1].y - nodes[0].y };
+        if (antiNodeIsValid(antiNode1, width, height)) {
+            try response.append(antiNode1);
+        }
+    }
+
+    if (2 * nodes[0].x >= nodes[1].x and 2 * nodes[0].y >= nodes[1].y) {
+        const antiNode2 = Point{ .x = 2 * nodes[0].x - nodes[1].x, .y = 2 * nodes[0].y - nodes[1].y };
+        if (antiNodeIsValid(antiNode2, width, height)) {
+            try response.append(antiNode2);
+        }
+    }
+
+    return response.toOwnedSlice();
+}
+
+fn antiNodeIsValid(antiNode: Point, width: usize, height: usize) bool {
+    // Don't technically need to check for >= 0 because that's already checked in `findAntinodes` (because otherwise
+    // there would be integer overflow by daring to use a negative number :P ), but doesn't hurt to replicate it here -
+    // otherwise a future reader might think we've forgotten it.
+    return antiNode.x >= 0 and antiNode.y >= 0 and antiNode.x < width and antiNode.y < height;
+}
+
+const expect = std.testing.expect;
+
+test "part_one" {
+    const part_one_response = try part_one(true);
+    print("DEBUG - part_one_response is {}\n", .{part_one_response});
+    try expect(part_one_response == 14);
+}