From d6ef49af270183a29776def2f1c3178fa14bc5aa Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Mon, 18 Dec 2023 07:42:05 +0000
Subject: Day 11 pt1

---
 day11.zig | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 day11.zig

(limited to 'day11.zig')

diff --git a/day11.zig b/day11.zig
new file mode 100644
index 0000000..bcb5c2a
--- /dev/null
+++ b/day11.zig
@@ -0,0 +1,96 @@
+const std = @import("std");
+
+pub fn main() !void {
+    try std.fmt.format(std.io.getStdOut().writer(), "day 11 pt1: {}\n", .{try solve_pt1(std.heap.page_allocator, puzzle_input)});
+}
+
+const Coord = struct {
+    x: usize,
+    y: usize,
+};
+
+inline fn get(grid: []const u8, width: usize, x: usize, y: usize) u8 {
+    return grid[y*(width+1) + x];
+}
+
+fn solve_pt1(a: std.mem.Allocator, input: []const u8) !u64 {
+    const width: usize = std.mem.indexOfScalar(u8, input, '\n') orelse return error.BadInput;
+    const height: usize = (input.len / width + 1) - 1;
+    // std.log.warn("width {} height {}", .{width, height});
+    const x_adjust = try a.alloc(usize, width);
+    defer a.free(x_adjust);
+    const y_adjust = try a.alloc(usize, height);
+    defer a.free(y_adjust);
+    var galaxies = std.ArrayList(Coord).init(a);
+    defer galaxies.deinit();
+    var x_adj: usize = 0;
+    for (0..width) |x| {
+        var allspace = true;
+        for (0..height) |y| {
+            const ch = get(input, width, x, y);
+            if (ch == '#') {
+                try galaxies.append(.{.x = x, .y = y});
+                allspace = false;
+            }
+        }
+        if (allspace) {
+            x_adj += 1;
+        }
+        x_adjust[x] = x_adj;
+    }
+    var y_adj:usize = 0;
+    for (0..height) |y| {
+        var allspace = true;
+        for (0..width) |x| {
+            const ch = get(input, width, x, y);
+            if (ch == '#') {
+                allspace = false;
+            }
+        }
+        if (allspace) {
+            y_adj += 1;
+        }
+        y_adjust[y] = y_adj;
+    }
+
+    for (galaxies.items) |*gal| {
+        const x = gal.x;
+        const y = gal.y;
+        gal.* = .{
+            .x = x + x_adjust[x],
+            .y = y + y_adjust[y],
+        };
+    }
+
+    var sum: usize = 0;
+    for (0..galaxies.items.len) |ix1| {
+        for (ix1..galaxies.items.len) |ix2| {
+            const g1 = galaxies.items[ix1];
+            const g2 = galaxies.items[ix2];
+            const x_diff = @max(g1.x, g2.x) - @min(g1.x, g2.x);
+            const y_diff = @max(g1.y, g2.y) - @min(g1.y, g2.y);
+            sum += x_diff + y_diff;
+        }
+    }
+
+    return sum;
+}
+
+test "pt1" {
+    try std.testing.expectEqual(@as(u64, 374), try solve_pt1(std.testing.allocator, test_input));
+}
+
+const test_input = 
+\\...#......
+\\.......#..
+\\#.........
+\\..........
+\\......#...
+\\.#........
+\\.........#
+\\..........
+\\.......#..
+\\#...#.....
+;
+
+const puzzle_input = @embedFile("day11.in");
\ No newline at end of file
-- 
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