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Perform updates in-place

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Bert Peters
2021-12-29 15:29:21 +01:00
parent 07e03c1630
commit 9dacb4c1ae
1 changed files with 31 additions and 18 deletions
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49
2021/src/day25.rs
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@@ -12,37 +12,50 @@ fn read_input(input: &mut dyn Read) -> (usize, Vec<u8>) {
fn advance(width: usize, state: &mut [u8]) -> bool {
debug_assert_eq!(state.len() % width, 0);
let mut helper = state.to_owned();
let mut changes = false;
// Move the eastbound herd
for (src, dest) in state
.chunks_exact(width)
.zip(helper.chunks_exact_mut(width))
{
for x in 0..width {
if src[x] == b'>' && src[(x + 1) % width] == b'.' {
dest[x] = b'.';
dest[(x + 1) % width] = b'>';
for src in state.chunks_exact_mut(width) {
let swap_last = src[0] == b'.' && src[width - 1] == b'>';
let mut x = 0;
while x < src.len() - 1 {
if src[x] == b'>' && src[x + 1] == b'.' {
src.swap(x, x + 1);
changes = true;
x += 2;
} else {
x += 1;
}
}
if swap_last {
src.swap(0, width - 1);
changes = true;
}
}
state.copy_from_slice(&helper);
// Now the southbound herd. Y in the outer loop for better cache locality
for y_offset in (0..helper.len()).step_by(width) {
let n_offset = (y_offset + width) % helper.len();
for x in 0..width {
let last_index = state.len() - width + x;
let swap_last = state[x] == b'.' && state[last_index] == b'v';
for x in 0..width {
if helper[x + y_offset] == b'v' && helper[x + n_offset] == b'.' {
state[x + y_offset] = b'.';
state[x + n_offset] = b'v';
let mut offset = x;
while offset < state.len() - width {
if state[offset] == b'v' && state[offset + width] == b'.' {
state.swap(offset, offset + width);
changes = true;
offset += 2 * width;
} else {
offset += width;
}
}
if swap_last {
state.swap(x, last_index);
changes = true;
}
}
changes