2022-05 in zig

2022/05-supply-stacks/first.zig

@@ -0,0 +1,62 @@
+const std = @import("std");
+
+const example = @embedFile("example");
+const input = @embedFile("input");
+
+pub fn main() anyerror!void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    var output = try solve(example, allocator);
+    try std.testing.expect(std.mem.eql(u8, output, "CMZ"));
+
+    const result = try solve(input, allocator);
+    try std.io.getStdOut().writer().print("{s}\n", .{result});
+}
+
+fn solve(puzzle: []const u8, allocator: std.mem.Allocator) ![]u8 {
+    var it = std.mem.tokenize(u8, puzzle, "\n");
+    var line = it.next() orelse unreachable;
+    // Initializations from the first line
+    const size = (line.len + 1) / 4;
+    var output = try allocator.alloc(u8, size);
+    var stacks = try allocator.alloc(std.ArrayList(u8), size);
+    for (stacks) |*stack| {
+        stack.* = std.ArrayList(u8).init(allocator);
+    }
+    // parse stacks
+    while (true) {
+        var i: usize = 0;
+        while (i < size) : (i += 1) {
+            const v = line[i * 4 + 1];
+            if (v != ' ') {
+                try stacks[i].insert(0, v);
+            }
+        }
+        line = it.next() orelse unreachable;
+        if (line[0] != '[') { // we got the line with numbers
+            break;
+        }
+    }
+    // process rules
+    while (it.next()) |l| {
+        var elts = std.mem.split(u8, l, " ");
+        _ = elts.next() orelse unreachable; // the move word
+        var n = try std.fmt.parseInt(u8, elts.next() orelse unreachable, 10);
+        _ = elts.next() orelse unreachable; // the from word
+        const s = try std.fmt.parseInt(u8, elts.next() orelse unreachable, 10) - 1;
+        _ = elts.next() orelse unreachable; // the to word
+        const d = try std.fmt.parseInt(u8, elts.next() orelse unreachable, 10) - 1;
+        while (n > 0) : (n -= 1) {
+            const v = stacks[s].pop();
+            try stacks[d].append(v);
+        }
+    }
+    // generate output
+    var i: usize = 0;
+    while (i < size) : (i += 1) {
+        output[i] = stacks[i].pop();
+    }
+    return output;
+}