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diff: fix LCS when a line/word/byte has been moved later

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This commit is contained in:
Martin von Zweigbergk 2021-04-28 22:41:20 -07:00
parent 13134bd5a4
commit 5b18e89a4d
1 changed files with 24 additions and 9 deletions
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33
lib/src/diff.rs
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@ -160,26 +160,33 @@ fn find_lcs(input: &[usize]) -> Vec<(usize, usize)> {
}
let mut chain = vec![(0, 0, 0); input.len()];
let mut longest = 0;
let mut longest_right_pos = 0;
let mut global_longest = 0;
let mut global_longest_right_pos = 0;
for (right_pos, &left_pos) in input.iter().enumerate() {
chain[right_pos] = (1, left_pos, usize::MAX);
let mut longest_from_here = 1;
let mut previous_right_pos = usize::MAX;
for i in (0..right_pos).rev() {
let (previous_len, previous_left_pos, _) = chain[i];
if previous_left_pos < left_pos {
let len = previous_len + 1;
chain[right_pos] = (len, left_pos, i);
if len > longest {
longest = len;
longest_right_pos = right_pos;
if len > longest_from_here {
longest_from_here = len;
previous_right_pos = i;
if len > global_longest {
global_longest = len;
global_longest_right_pos = right_pos;
// If this is the longest chain globally so far, we cannot find a
// longer one by using a previous value, so break early.
break;
}
}
break;
}
}
chain[right_pos] = (longest_from_here, left_pos, previous_right_pos);
}
let mut result = vec![];
let mut right_pos = longest_right_pos;
let mut right_pos = global_longest_right_pos;
loop {
let (_, left_pos, previous_right_pos) = chain[right_pos];
result.push((left_pos, right_pos));
@ -578,6 +585,14 @@ mod tests {
);
}
#[test]
fn test_find_lcs_element_moved_later() {
assert_eq!(
find_lcs(&[0, 1, 3, 4, 2, 5, 6]),
vec![(0, 0), (1, 1), (3, 2), (4, 3), (5, 5), (6, 6)]
);
}
#[test]
fn test_find_lcs_interleaved_longest_chains() {
assert_eq!(