Solution to 19-2

inputs/19/real.txt

@@ -399,4 +399,4 @@ rbgruwuugbgbrgrgugrgrrrwruuggubbwrbruubbbr
 rrrrwugrrrrrubrbrgwgrrgwrubgwuuuburburburwrrgbwu
 ruwgugbguwuwgrwbrbgwruwurbugwwgbwwugbrrbwguur
 ugrrwbbwwbwwbbururwguuwwurwrguggggugrwbugwwgwgg
-gbwurruuubuurrwurbuwwwubbwbwbbrgrbrwbbwrrrbruwrwubbrbgwbwb
+gbwurruuubuurrwurbuwwwubbwbwbbrgrbrwbbwrrrbruwrwubbrbgwbwb

solutions/19.zig

@@ -9,7 +9,7 @@ pub fn main() !void {
     defer _ = gpa.deinit();
     const allocator = gpa.allocator();
 
-    const response = try partOne(false, false, allocator);
+    const response = try partTwo(false, false, allocator);
     print("{}\n", .{response});
 }
 
@@ -26,6 +26,8 @@ fn partOne(is_test_case: bool, debug: bool, allocator: std.mem.Allocator) !u16 {
 
     var known_valid_designs = std.StringHashMap(void).init(allocator);
     defer known_valid_designs.deinit();
+    // I added in this minor optimization because my code was running _super_ slow and I couldn't figure out why.
+    // Then I realized I'd acccidentally left in a `std.time.sleep(1000000000)` that I'd introduced while debugging :P
     var known_invalid_designs = std.StringHashMap(void).init(allocator);
     defer known_invalid_designs.deinit();
     for (towels) |towel| {
@@ -77,12 +79,68 @@ fn parseTowels(line: []const u8, allocator: std.mem.Allocator) [][]const u8 {
     return response.toOwnedSlice() catch unreachable;
 }
 
-test "partOne" {
+// test "partOne" {
+//     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+//     defer _ = gpa.deinit();
+//     const allocator = gpa.allocator();
+
+//     const response = try partOne(true, true, allocator);
+//     print("Part One response is {}\n", .{response});
+//     try expect(response == 6);
+// }
+
+fn partTwo(is_test_case: bool, debug: bool, allocator: std.mem.Allocator) !u128 {
+    const input_file = try util.getInputFile("19", is_test_case);
+    const data = try util.readAllInputWithAllocator(input_file, allocator);
+    defer allocator.free(data);
+
+    var data_lines_it = std.mem.splitScalar(u8, data, '\n');
+    const towels = parseTowels(data_lines_it.next().?, allocator);
+    defer allocator.free(towels);
+
+    _ = data_lines_it.next();
+
+    var ways_to_make_designs = std.StringHashMap(u128).init(allocator);
+    defer ways_to_make_designs.deinit();
+    // Not priming the "ways to make design" count, here, because this isn't as simple as the boolean yes-no in the
+    // previous case - e.g. if we have towels `rbr`, `r`, and `br`, then the count for `rbr` should be 2, not 1.
+
+    var count: u128 = 0;
+    while (data_lines_it.next()) |design| {
+        const ways = waysToMakeDesign(design, towels, &ways_to_make_designs, debug);
+        print("Found {} ways to make {s}\n", .{ ways, design });
+        count += ways;
+    }
+    return count;
+}
+
+fn waysToMakeDesign(design: []const u8, towels: [][]const u8, ways_to_make_designs: *std.StringHashMap(u128), debug: bool) u128 {
+    if (design.len == 0) {
+        return 1;
+    }
+    if (!(ways_to_make_designs.contains(design))) {
+        var accum: u128 = 0;
+        for (towels) |towel| {
+            if (design.len >= towel.len and std.mem.eql(u8, towel, design[0..towel.len])) {
+                const remainder = design[towel.len..];
+                const response = waysToMakeDesign(remainder, towels, ways_to_make_designs, debug);
+                if (response > 0) {
+                    log("Got response {} to add to accum {} for remainder {s}\n", .{ response, accum, remainder }, debug);
+                    accum += response;
+                }
+            }
+        }
+        ways_to_make_designs.put(design, accum) catch unreachable;
+    }
+    return ways_to_make_designs.get(design).?;
+}
+
+test "partTwo" {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
     defer _ = gpa.deinit();
     const allocator = gpa.allocator();
 
-    const response = try partOne(true, true, allocator);
-    print("Part One response is {}\n", .{response});
-    try expect(response == 6);
+    const response = try partTwo(true, true, allocator);
+    print("Part Two response is {}\n", .{response});
+    try expect(response == 16);
 }