nesv.ca
My Advent of Code 2025 solutions
Day 3: Lobby
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src/day03.zig
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src/day03.zig
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const std = @import("std");
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const mem = std.mem;
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const testing = std.testing;
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const aoc = @import("advent_of_code_2025");
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const input = @embedFile("input03.txt");
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pub fn main() !void {
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var max_joltage_2: u64 = 0;
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var max_joltage_12: u64 = 0;
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var banks = mem.tokenizeScalar(u8, input, '\n');
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while (banks.next()) |bank| {
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max_joltage_2 += maxJoltage(bank, 2);
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max_joltage_12 += maxJoltage(bank, 12);
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}
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std.debug.print("{d}\n{d}\n", .{
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max_joltage_2,
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max_joltage_12,
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});
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}
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// Find the maximum joltage rating for a battery bank by enabling the specified
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// number of batteries.
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fn maxJoltage(bank: []const u8, num_batteries: usize) u64 {
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var max: u64 = 0;
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var start: usize = 0;
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var remaining = num_batteries;
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while (remaining > 0) : (remaining -= 1) {
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// Take a slice of the battery bank, so that we are only looking at
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// `bank.len - remaining` values. In the best-case scenario, the
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// largest value we find is at the end of the slice.
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const end = bank.len - remaining + 1;
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const batteries = bank[start..end];
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const index = mem.indexOfMax(u8, batteries);
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const joltage: u64 = @intCast(batteries[index] - '0');
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max = (max * 10) + joltage;
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// On the next iteration, start at the index after the current max
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// value.
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start += index + 1;
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}
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return max;
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}
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const test_input = [_][]const u8{
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"987654321111111",
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"811111111111119",
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"234234234234278",
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"818181911112111",
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};
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test maxJoltage {
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try testing.expectEqual(98, maxJoltage(test_input[0], 2));
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try testing.expectEqual(89, maxJoltage(test_input[1], 2));
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try testing.expectEqual(78, maxJoltage(test_input[2], 2));
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try testing.expectEqual(92, maxJoltage(test_input[3], 2));
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try testing.expectEqual(987654321111, maxJoltage(test_input[0], 12));
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try testing.expectEqual(811111111119, maxJoltage(test_input[1], 12));
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try testing.expectEqual(434234234278, maxJoltage(test_input[2], 12));
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try testing.expectEqual(888911112111, maxJoltage(test_input[3], 12));
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}