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Reduce dimensions of DP memo

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We don't actually need all days, we just need the previous to build the
next
This commit is contained in:
Bert Peters
2023-12-12 18:14:32 +01:00
parent 83d14af4f3
commit e449672487
1 changed files with 17 additions and 9 deletions
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26
2023/src/day12.rs
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@@ -1,3 +1,5 @@
use std::mem;
use nom::bytes::complete::tag; use nom::bytes::complete::tag;
use nom::bytes::complete::take_until; use nom::bytes::complete::take_until;
use nom::multi::many1; use nom::multi::many1;
@@ -13,36 +15,42 @@ fn number_ways(line: &[u8], groups: &[u8]) -> u64 {
return 0; return 0;
}; };
let mut dp = vec![vec![vec![0; max_group as usize + 1]; groups.len() + 1]; line.len() + 1]; let mut next = vec![vec![0; max_group as usize + 1]; groups.len() + 1];
dp[0][0][0] = 1; let mut cur = next.clone();
cur[0][0] = 1;
for &c in line {
for entry in &mut next {
entry.fill(0);
}
for (line_pos, &c) in line.iter().enumerate() {
for group_pos in 0..=groups.len() { for group_pos in 0..=groups.len() {
let group = *groups.get(group_pos).unwrap_or(&0); let group = *groups.get(group_pos).unwrap_or(&0);
for cur_group in 0..=max_group { for cur_group in 0..=max_group {
let ways = dp[line_pos][group_pos][cur_group as usize]; let ways = cur[group_pos][cur_group as usize];
if ways == 0 { if ways == 0 {
continue; continue;
} }
// Either defective or maybe defective // Either defective or maybe defective
if c != b'.' && cur_group < group { if c != b'.' && cur_group < group {
dp[line_pos + 1][group_pos][cur_group as usize + 1] += ways; next[group_pos][cur_group as usize + 1] += ways;
} }
if c != b'#' { if c != b'#' {
if cur_group == 0 { if cur_group == 0 {
dp[line_pos + 1][group_pos][0] += ways; next[group_pos][0] += ways;
} else if group == cur_group { } else if group == cur_group {
dp[line_pos + 1][group_pos + 1][0] += ways; next[group_pos + 1][0] += ways;
} }
} }
} }
} }
mem::swap(&mut cur, &mut next);
} }
dp[line.len()][groups.len()][0] cur[groups.len()][0] + cur[groups.len() - 1][groups[groups.len() - 1] as usize]
+ dp[line.len()][groups.len() - 1][groups[groups.len() - 1] as usize]
} }
fn parse_lines(i: &[u8]) -> IResult<&[u8], Vec<(&[u8], Vec<u8>)>> { fn parse_lines(i: &[u8]) -> IResult<&[u8], Vec<(&[u8], Vec<u8>)>> {