So much easier than day10. Man this year is crazy

day11/data.txt

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day11/main.zig

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+const std = @import("std");
+
+const Galaxy = struct { row: usize, col: usize };
+
+pub fn main() !void {
+    const content = @embedFile("data.txt");
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const allocator = gpa.allocator();
+
+    // put into ArrayList of ArrayLists
+    var grid = try parseGrid(content, allocator);
+    defer grid.deinit();
+    std.debug.print("grid: {any}\n", .{grid});
+
+    // find empty rows
+    const emptyRows = try findEmptyRows(grid, allocator);
+    std.debug.print("empty rows: {any}\n", .{emptyRows});
+
+    // find empty columns
+    const emptyColumns = try findEmptyColumns(grid, allocator);
+    std.debug.print("empty cols: {any}\n", .{emptyColumns});
+
+    // duplicate empty rows
+    // NOTE: not doing this any more, using Part 2 solution for Part 1
+    //
+    // for (emptyRows.items, 0..) |row, i| {
+    //     try grid.insert(row + i, grid.items[row + i]);
+    // }
+    //
+    // // duplicate empty columns
+    // for (emptyColumns.items, 0..) |col, i| {
+    //     for (grid.items, 0..) |_, row| {
+    //         try grid.items[row].insert(col + i, '.');
+    //     }
+    // }
+
+    // find original galaxy locations
+    var galaxies = std.ArrayList(Galaxy).init(allocator);
+    for (grid.items, 0..) |row, i| {
+        for (row.items, 0..) |char, j| {
+            if (char == '#') {
+                try galaxies.append(Galaxy{ .row = i, .col = j });
+            }
+        }
+    }
+
+    var galaxies1 = std.ArrayList(Galaxy).init(allocator);
+    var galaxies2 = std.ArrayList(Galaxy).init(allocator);
+
+    for (galaxies.items) |g| {
+        const row = g.row;
+        const col = g.col;
+
+        // how many expanded rows & cols before this galaxy?
+        var expandedRows: usize = 0;
+        for (emptyRows.items) |r| {
+            if (r > row) {
+                break;
+            }
+            expandedRows += 1;
+        }
+
+        var expandedColumns: usize = 0;
+        for (emptyColumns.items) |c| {
+            if (c > col) {
+                break;
+            }
+            expandedColumns += 1;
+        }
+
+        const expansionFactor = 1_000_000;
+
+        try galaxies1.append(Galaxy{ .row = row + expandedRows, .col = col + expandedColumns });
+        try galaxies2.append(Galaxy{ .row = row + (expansionFactor - 1) * expandedRows, .col = col + (expansionFactor - 1) * expandedColumns });
+    }
+
+    // add up all their distances
+    var part1: usize = 0;
+    for (0..galaxies1.items.len - 1) |i| {
+        for (i + 1..galaxies1.items.len) |j| {
+            part1 += dist(galaxies1.items[j], galaxies1.items[i]);
+        }
+    }
+
+    std.debug.print("Part 1: {d}\n", .{part1});
+
+    var part2: usize = 0;
+    for (0..galaxies2.items.len - 1) |i| {
+        for (i + 1..galaxies2.items.len) |j| {
+            part2 += dist(galaxies2.items[j], galaxies2.items[i]);
+        }
+    }
+
+    std.debug.print("Part 2: {d}\n", .{part2});
+}
+
+fn dist(a: Galaxy, b: Galaxy) usize {
+    const x = if (a.row > b.row) a.row - b.row else b.row - a.row;
+    const y = if (a.col > b.col) a.col - b.col else b.col - a.col;
+    return x + y;
+}
+
+fn findEmptyColumns(grid: std.ArrayList(std.ArrayList(u8)), allocator: std.mem.Allocator) !std.ArrayList(usize) {
+    var cols = std.ArrayList(usize).init(allocator);
+    const height = grid.items.len;
+    const width = grid.items[0].items.len;
+
+    for (0..width) |col| {
+        var allEmpty = true;
+        for (0..height) |row| {
+            if (grid.items[row].items[col] == '#') {
+                allEmpty = false;
+            }
+        }
+        if (allEmpty) {
+            try cols.append(col);
+        }
+    }
+    return cols;
+}
+
+fn findEmptyRows(grid: std.ArrayList(std.ArrayList(u8)), allocator: std.mem.Allocator) !std.ArrayList(usize) {
+    var rows = std.ArrayList(usize).init(allocator);
+
+    for (grid.items, 0..) |row, idx| {
+        var allEmpty = true;
+        for (row.items) |char| {
+            if (char == '#') {
+                allEmpty = false;
+            }
+        }
+        if (allEmpty) {
+            try rows.append(idx);
+        }
+    }
+    return rows;
+}
+
+fn parseGrid(content: []const u8, allocator: std.mem.Allocator) !std.ArrayList(std.ArrayList(u8)) {
+    var grid = std.ArrayList(std.ArrayList(u8)).init(allocator);
+    var lines = std.mem.split(u8, content, "\n");
+
+    while (lines.next()) |line| {
+        if (line.len < 1) {
+            break;
+        }
+
+        var al = std.ArrayList(u8).init(allocator);
+        for (line) |char| {
+            try al.append(char);
+        }
+
+        try grid.append(al);
+    }
+
+    return grid;
+}

day11/test.txt

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+...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....