93 lines
2.8 KiB
Zig
93 lines
2.8 KiB
Zig
const std = @import("std");
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const example = @embedFile("example");
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const input = @embedFile("input");
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pub fn main() anyerror!void {
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var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
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defer arena.deinit();
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const allocator = arena.allocator();
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try std.testing.expectEqual(try solve(example, allocator), 31);
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const result = try solve(input, allocator);
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try std.io.getStdOut().writer().print("{}\n", .{result});
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}
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const Node = struct {
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x: u8,
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y: u8,
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cost: ?u64,
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value: u8,
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fn evalAndAdd(e: *Node, n: *Node, nq: *std.PriorityQueue(*Node, void, lesserThan)) !void {
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if (e.cost == null and e.value <= n.value + 1) {
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e.cost = n.cost.? + 1;
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try nq.add(e);
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}
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}
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};
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fn lesserThan(context: void, a: *Node, b: *Node) std.math.Order {
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_ = context;
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return std.math.order(a.cost.?, b.cost.?);
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}
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fn solve(puzzle: []const u8, allocator: std.mem.Allocator) !u64 {
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var it = std.mem.tokenize(u8, puzzle, "\n");
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var grid = std.ArrayList(std.ArrayList(Node)).init(allocator);
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var Sx: u8 = undefined;
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var Sy: u8 = undefined;
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var Ex: u8 = undefined;
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var Ey: u8 = undefined;
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// process input
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var y: u8 = 0;
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var line = it.next() orelse unreachable;
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const width = line.len;
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while (true) : (line = it.next() orelse break) {
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var l = try grid.addOne();
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l.* = try std.ArrayList(Node).initCapacity(allocator, width);
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var x: u8 = 0;
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while (x < line.len) : (x += 1) {
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var n = l.*.addOneAssumeCapacity();
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n.*.x = x;
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n.*.y = y;
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n.*.cost = null;
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n.*.value = switch (line[x]) {
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'S' => blk: {
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Sx = x;
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Sy = y;
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n.*.cost = 0;
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break :blk 'a';
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},
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'E' => blk: {
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Ex = x;
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Ey = y;
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break :blk 'z';
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},
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else => line[x],
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};
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}
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y += 1;
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}
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const height = grid.items.len;
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// find shortest path
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var nq = std.PriorityQueue(*Node, void, lesserThan).init(allocator, {});
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try nq.add(&grid.items[Sy].items[Sx]);
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while (true) {
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var n = nq.remove();
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if (n.x == Ex and n.y == Ey) {
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return n.cost.?;
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}
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if (n.x > 0) {
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try grid.items[n.y].items[n.x - 1].evalAndAdd(n, &nq);
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}
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if (n.x < width - 1) {
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try grid.items[n.y].items[n.x + 1].evalAndAdd(n, &nq);
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}
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if (n.y > 0) {
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try grid.items[n.y - 1].items[n.x].evalAndAdd(n, &nq);
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}
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if (n.y < height - 1) {
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try grid.items[n.y + 1].items[n.x].evalAndAdd(n, &nq);
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}
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}
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}
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