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138 lines
3.3 KiB
138 lines
3.3 KiB
const std = @import("std");
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fn StackList(comptime T: type, comptime capacity_type: type, comptime capacity: capacity_type) type {
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return struct {
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const Self = @This();
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mem: [capacity]T,
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length: capacity_type,
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fn add(self: *Self, value: T) void {
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self.mem[self.length] = value;
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self.length += 1;
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}
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fn has(self: *Self, needle: T) bool {
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for (0..self.length) |i| {
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if (self.mem[i] == needle) {
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return true;
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}
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}
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return false;
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}
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fn getMutableSlice(self: *Self) []T {
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return (&self.mem)[0..self.length];
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}
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fn getSlice(self: *const Self) []const T {
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return self.mem[0..self.length];
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}
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fn init() Self {
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return Self{
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.mem = undefined,
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.length = 0,
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};
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}
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};
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}
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fn addDigit(result: anytype, digit: u8) void {
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result.* = (result.* * 10) + (digit - '0');
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}
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fn canStartWithGroup(springs: []const u8, group_size: usize) bool {
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if (springs.len < group_size) {
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return false;
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}
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if (springs.len > group_size and springs[group_size] == '#') {
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return false;
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}
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var i: usize = 0;
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while (i < group_size) : (i += 1) {
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if (springs[i] == '.') {
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return false;
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}
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}
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return true;
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}
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fn solveBackward(readings: []i64) i64 {
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var i: usize = 1;
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while (i < readings.len) : (i += 1) {
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var j = readings.len - 1;
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while (j >= i) : (j -= 1) {
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readings[j] = readings[j] - readings[j - 1];
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}
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}
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var result: i64 = 0;
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var sign: i64 = 1;
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for (readings) |value| {
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result += sign * value;
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sign *= -1;
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}
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//std.debug.print("backwards: derivatives: {any}, result: {d}\n", .{ readings, result });
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return result;
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}
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fn solveForward(readings: []i64) i64 {
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var i: usize = 1;
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while (i < readings.len) : (i += 1) {
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var j: usize = 0;
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while (j < readings.len - i) : (j += 1) {
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readings[j] = readings[j + 1] - readings[j];
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}
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}
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var result: i64 = 0;
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for (readings) |value| {
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result += value;
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}
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//std.debug.print("forwards: derivatives: {any}, result: {d}\n", .{ readings, result });
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return result;
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}
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fn solveLine(line: []const u8) i64 {
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var i: usize = 0;
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var readings = StackList(i64, usize, 31).init();
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while (i < line.len) {
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var number: i64 = 0;
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var is_negative = false;
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if (line[i] == '-') {
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is_negative = true;
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i += 1;
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}
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while (i < line.len and line[i] != ' ') : (i += 1) {
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addDigit(&number, line[i]);
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}
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if (is_negative) {
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number = -number;
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}
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readings.add(number);
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i += 1;
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}
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return solveBackward(readings.getMutableSlice());
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}
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pub fn main() !void {
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const stdout = std.io.getStdOut().writer();
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const raw_in = std.io.getStdIn();
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var buffered_reader = std.io.bufferedReader(raw_in.reader());
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var reader = buffered_reader.reader();
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var result: i64 = 0;
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var line_buffer: [1000]u8 = undefined;
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while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
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result += solveLine(line);
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}
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try stdout.print("{d}\n", .{result});
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}
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