probably made it a bit faster

day12/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day12"
+version = "0.1.0"

day12/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "day12"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day12/src/main.rs

@@ -0,0 +1,247 @@
+use std::fs::read_to_string;
+use std::time::Instant;
+use std::iter;
+
+// Counts all options by advancing through the spring layout from left to right, splitting at
+// possible uncertainities. Groups sequences of uncertain values and uses combinatorics.
+fn count_options(layout: &[u8], broken_sequences: &[u32], sum_broken: u32) -> u64 {
+    // Assuming sum_broken must be sum of broken_sequences
+    // If no more broken need to be placed, the remaining are all unbroken
+    if sum_broken == 0 {
+        // If the remaining data contains a surely broken spring, the configuration is impossible
+        if layout.contains(&b'#') {
+            return 0;
+        }
+        // The rest are not broken, 1 option
+        return 1;
+    }
+    // Go ahead in the layout to find place where a split of options is
+    let mut split_position = 0;
+    // Skip through all unbroken
+    while split_position < layout.len() && layout[split_position] == b'.' {
+        split_position += 1;
+    }
+    // Found no place to fit remaining broken springs, impossible
+    if layout.len() - split_position < sum_broken as usize + broken_sequences.len() - 1 {
+        return 0;
+    }
+    // Count amount of uncertain springs (can be zero)
+    let mut num_uncertain: usize = 0;
+    while split_position < layout.len() && layout[split_position] == b'?' {
+        split_position += 1;
+        num_uncertain += 1;
+    }
+    if split_position == layout.len() || layout[split_position] == b'.' {
+        // Block of 1 or more uncertain springs followed by a unbroken spring
+        let mut sum_options = 0;
+        // Initially try assuming all the question marks will be unbroken
+        if split_position < layout.len() {
+            sum_options += count_options(&layout[split_position + 1..], broken_sequences, sum_broken);
+        }
+        // Taking some number of elements from broken sequences
+        let mut num_elems_taken = 1;
+        let mut sum_elems_taken = broken_sequences[0];
+        while num_elems_taken <= broken_sequences.len() && sum_elems_taken as usize + num_elems_taken - 1 <= num_uncertain {
+            // If the split was done due to end of input, it's the length, otherwise advance by 1
+            let corrected_split_position = std::cmp::min(split_position + 1, layout.len());
+            // Multiplying the combination of elements before with recursive options after
+            let pre_split_options = count_options_in_uncertain(num_uncertain as u64, sum_elems_taken as u64, num_elems_taken as u64);
+            let post_split_options = count_options(
+                &layout[corrected_split_position..],
+                &broken_sequences[num_elems_taken..], sum_broken - sum_elems_taken);
+            sum_options += pre_split_options * post_split_options;
+            // Prepare for the next iteration
+            if num_elems_taken < broken_sequences.len() {
+                sum_elems_taken += broken_sequences[num_elems_taken];
+            }
+            num_elems_taken += 1;
+        }
+        return sum_options;
+    } else {
+        // Block of 0 or more uncertain springs followed by at least one broken spring
+        let mut sum_options = 0;
+        // Count how many known broken elements there are after the uncertain
+        let mut last_min_length = 0;
+        while split_position < layout.len() && layout[split_position] == b'#' {
+            split_position += 1;
+            last_min_length += 1;
+        }
+        let extended_num_uncertain = num_uncertain + last_min_length;
+        // Taking some number of elements from broken sequences
+        let mut last_taken_index = 0;
+        let mut sum_elems_taken_no_last: u32 = 0;
+        while last_taken_index < broken_sequences.len() {
+            // Length of last element that is taken, we need to fit it around the end of the region
+            let last_length = broken_sequences[last_taken_index];
+            // Putting the last elem at some offset, subtracted from split_position
+            let mut last_offset = last_min_length;
+            while last_offset <= last_length as usize && last_offset <= extended_num_uncertain {
+                // If sum of taken elements with free spaces (last_taken_index) doesn't fit in the
+                // uncertainity region
+                if sum_elems_taken_no_last as usize + last_taken_index > extended_num_uncertain - last_offset {
+                    break;
+                }
+                // Multiplying the combination of elements before with recursive options after
+                let pre_split_options;
+                if extended_num_uncertain > last_offset + 1 {
+                    pre_split_options = count_options_in_uncertain(
+                        (extended_num_uncertain - last_offset - 1) as u64, sum_elems_taken_no_last as u64, last_taken_index as u64);
+                } else {
+                    pre_split_options = 1;
+                }
+                let post_split_options = count_options_consume_sequence(
+                    &layout[split_position - last_offset..],
+                    &broken_sequences[last_taken_index..], sum_broken - sum_elems_taken_no_last);
+                sum_options += pre_split_options * post_split_options;
+                // Prepare for the next iteration
+                last_offset += 1;
+            }
+            // Prepare for the next iteration
+            sum_elems_taken_no_last += broken_sequences[last_taken_index];
+            last_taken_index += 1;
+        }
+        return sum_options;
+    }
+}
+
+fn choose(n: u64, k: u64) -> u64 {
+    let mut prod = 1;
+    let mut n_copy = n;
+    for i in 1..=k {
+        prod *= n_copy;
+        n_copy -= 1;
+        prod /= i;
+    }
+    prod
+}
+
+fn count_options_in_uncertain(length_uncertain: u64, sum_broken: u64, num_broken: u64) -> u64 {
+    let slots = length_uncertain - sum_broken + 1;
+    // slots choose num_broken
+    if slots == 0 || num_broken == 0 {
+        return 1;
+    }
+    choose(slots, num_broken)
+}
+
+// Helper function for count_options, assuming that a sequence of broken springs starts at
+// the beginning of the slice and that sum_broken is sum of broken_sequences and is not 0
+fn count_options_consume_sequence(layout: &[u8], broken_sequences: &[u32], sum_broken: u32) -> u64 {
+    let mut sequence_position = 0usize;
+    let target_position = sequence_position + broken_sequences[0] as usize;
+    // If we'd run out of space trying to process this option, impossible
+    if target_position > layout.len() {
+        return 0;
+    }
+    // Go through all potentially broken elements
+    while sequence_position < target_position && layout[sequence_position] != b'.' {
+        sequence_position += 1;
+    }
+    // If found a surely unbroken element before end of sequence, impossible
+    if sequence_position < target_position {
+        return 0;
+    }
+    // If we aren't at the end of sequence
+    if sequence_position < layout.len() {
+        // If there's yet another surely broken spring, the sequence would be too long, impossible
+        if layout[sequence_position] == b'#' {
+            return 0;
+        }
+        // If there's a following unbroken element, advance through that because count_options
+        // assumes with each call that we're starting from a fresh potential sequence
+        sequence_position += 1;
+    }
+    // Call count_options recursively with advanced layout options and consumed one sequence
+    count_options(&layout[sequence_position..], &broken_sequences[1..],
+                  sum_broken - broken_sequences[0])
+}
+
+// Generate all configurations of replacing '?' with '#' or '.'
+fn generate_naive_options(layout: &[u8]) -> Vec<Vec<u8>> {
+    let mut split_position = 0;
+    while split_position < layout.len() && layout[split_position] != b'?' {
+        split_position += 1;
+    }
+    if split_position == layout.len() {
+        return vec![Vec::from(layout)];
+    }
+    let mut prefix1 = Vec::from(&layout[..=split_position]);
+    let mut prefix2 = Vec::from(&layout[..=split_position]);
+    prefix1[split_position] = b'#';
+    prefix2[split_position] = b'.';
+    let mut merged: Vec<Vec<u8>> = Vec::new();
+    let options = generate_naive_options(&layout[split_position + 1..]);
+    for option in options {
+        let mut prefix1_clone = prefix1.clone();
+        let mut prefix2_clone = prefix2.clone();
+        prefix1_clone.extend_from_slice(&option);
+        prefix2_clone.extend_from_slice(&option);
+        merged.push(prefix1_clone);
+        merged.push(prefix2_clone);
+    }
+    merged
+}
+
+// Generate all configurations and test them
+fn count_naive_options(layout: &[u8], broken_sequences: &[u32]) -> u32 {
+    let options = generate_naive_options(&layout);
+    options.iter().filter(|&option| {
+        let mut position = 0;
+        for &length in broken_sequences {
+            while position < option.len() && option[position] == b'.' {
+                position += 1;
+            }
+            let target_position = position + length as usize;
+            if target_position > option.len() {
+                return false;
+            }
+            while position < target_position && option[position] == b'#' {
+                position += 1;
+            }
+            if position != target_position {
+                return false;
+            }
+            if position < option.len() {
+                if option[position] == b'#' {
+                    return false;
+                }
+                position += 1;
+            }
+        }
+        while position < option.len() {
+            if option[position] != b'.' {
+                return false;
+            }
+            position += 1;
+        }
+        true
+    }).count() as u32
+}
+
+fn main() {
+    let time_start = Instant::now();
+    let input_str = read_to_string("input.txt").unwrap();
+    let time_start_no_io = Instant::now();
+    let mut sum1 = 0u64;
+    let mut sum2 = 0u64;
+    for line in input_str.lines() {
+        let mut split_whitespace = line.split_whitespace();
+        let layout_str = split_whitespace.next().unwrap();
+        let layout = layout_str.bytes().collect::<Vec<_>>();
+        let layout2 = layout_str.bytes().chain(iter::once(b'?')).cycle().take(layout.len() * 5 + 4).collect::<Vec<_>>();
+        let numbers = split_whitespace.next().unwrap()
+            .split(',').map(|str| str.parse::<u32>().unwrap()).collect::<Vec<_>>();
+        let numbers2 = numbers.iter().cycle().take(numbers.len() * 5).copied().collect::<Vec<_>>();
+        let sum_numbers = numbers.iter().sum::<u32>();
+        let sum_numbers2 = sum_numbers * 5;
+        let options = count_options(&layout, &numbers, sum_numbers) as u64;
+        sum1 += options;
+        sum2 += count_options(&layout2, &numbers2, sum_numbers2) as u64;
+    }
+    let elapsed = time_start.elapsed().as_micros();
+    let elapsed_no_io = time_start_no_io.elapsed().as_micros();
+    println!("Time: {}us", elapsed);
+    println!("Time without file i/o: {}us", elapsed_no_io);
+    println!("Sum1: {}", sum1);
+    println!("Sum2: {}", sum2);
+}