FEAT: Day10

AdventOfCode2023/src/day9/day9.zig

@@ -0,0 +1,66 @@
+const std = @import("std");
+const expect = std.testing.expect;
+const print = std.debug.print;
+
+fn isAllZeroes(nums: []i128) bool {
+    for (nums) |n| {
+        if (n != 0) {
+            return false;
+        }
+    }
+    return true;
+}
+
+fn nextNum(allocator: std.mem.Allocator, nums: []i128) !i128 {
+    if (isAllZeroes(nums)) {
+        return 0;
+    }
+
+    var diff = try allocator.alloc(i128, nums.len - 1);
+    for (0..nums.len - 1) |n| {
+        var d = nums[n + 1] - nums[n];
+        diff[n] = d;
+    }
+
+    return nums[nums.len - 1] + try nextNum(allocator, diff);
+}
+
+test "Next num finder" {
+    var allocator = std.heap.page_allocator;
+    var nums = [_]i128{ 0, 3, 6, 9, 12, 15 };
+    try expect(try nextNum(allocator, nums[0..]) == 18);
+
+    var nums2 = [_]i128{ 1, 3, 6, 10, 15, 21 };
+    try expect(try nextNum(allocator, nums2[0..]) == 28);
+
+    var nums3 = [_]i128{ 10, 13, 16, 21, 30, 45 };
+    try expect(try nextNum(allocator, nums3[0..]) == 68);
+}
+
+pub fn solve(input: [][]const u8) !void {
+    var allocator = std.heap.page_allocator;
+    var part1: i128 = 0;
+    var part2: i128 = 0;
+
+    for (input) |line| {
+        var list = std.ArrayList(i128).init(allocator);
+        var tokenizer = std.mem.tokenizeSequence(u8, line, " ");
+        while (tokenizer.next()) |n| {
+            try list.append(try std.fmt.parseInt(i128, n, 10));
+        }
+
+        var n1 = try nextNum(allocator, list.items);
+
+        std.mem.reverse(i128, list.items);
+
+        var n2 = try nextNum(allocator, list.items);
+
+        part1 += n1;
+        part2 += n2;
+
+        list.deinit();
+    }
+
+    print("Part 1: {}\n", .{part1});
+    print("Part 2: {}\n", .{part2});
+}