jsondiffpatch 0.1.0

JSON diff & patch (object and array diff, text diff, multiple output formats)
Documentation 
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//! This module implements the Longest Common Subsequence (LCS) algorithm.
//! The LCS problem is finding the longest subsequence common to two sequences.
//! It differs from the problem of finding common substrings: unlike substrings, subsequences
//! are not required to occupy consecutive positions within the original sequences.
//! This implementation handles Unicode strings efficiently and correctly, ensuring
//! that multi-byte characters are managed properly.

use serde_json::Value;

/// Computes the longest common subsequence of two input strings.
///
/// The longest common subsequence (LCS) of two strings is the longest sequence that can
/// be derived from both strings by deleting some elements without changing the order of
/// the remaining elements.
///
/// ## Note
/// The function may return different LCSs for the same pair of strings depending on the
/// order of the inputs and the nature of the sequences. This is due to the way the dynamic
/// programming algorithm resolves ties when multiple common subsequences of the same length
/// exist. The order of the input strings can influence the specific path taken through the
/// DP table, resulting in different valid LCS outputs.
///
///  For example:
/// `longest_common_subsequence("hello, world!", "world, hello!")` returns `"hello!"`
/// but
/// `longest_common_subsequence("world, hello!", "hello, world!")` returns `"world!"`
///
/// This difference arises because the dynamic programming table is filled differently based
/// on the input order, leading to different tie-breaking decisions and thus different LCS results.
pub fn longest_common_subsequence(
    first_seq: &[Value],
    second_seq: &[Value],
) -> Vec<(usize, usize)> {
    let lcs_lengths = initialize_lcs_lengths(first_seq, second_seq);

    reconstruct_lcs(first_seq, second_seq, &lcs_lengths)
}

fn initialize_lcs_lengths(first_seq: &[Value], second_seq: &[Value]) -> Vec<Vec<usize>> {
    let first_seq_len = first_seq.len();
    let second_seq_len = second_seq.len();

    let mut lcs_lengths = vec![vec![0; second_seq_len + 1]; first_seq_len + 1];

    // Populate the LCS lengths table
    (1..=first_seq_len).for_each(|i| {
        (1..=second_seq_len).for_each(|j| {
            lcs_lengths[i][j] = if first_seq[i - 1] == second_seq[j - 1] {
                lcs_lengths[i - 1][j - 1] + 1
            } else {
                lcs_lengths[i - 1][j].max(lcs_lengths[i][j - 1])
            };
        });
    });

    lcs_lengths
}

fn reconstruct_lcs(
    first_seq_chars: &[Value],
    second_seq_chars: &[Value],
    lcs_lengths: &[Vec<usize>],
) -> Vec<(usize, usize)> {
    let mut lcs_indices = Vec::new();
    let mut i = first_seq_chars.len();
    let mut j = second_seq_chars.len();
    while i > 0 && j > 0 {
        if first_seq_chars[i - 1] == second_seq_chars[j - 1] {
            lcs_indices.push((i - 1, j - 1));
            i -= 1;
            j -= 1;
        } else if lcs_lengths[i - 1][j] >= lcs_lengths[i][j - 1] {
            i -= 1;
        } else {
            j -= 1;
        }
    }

    lcs_indices.reverse();
    lcs_indices
}

// #[cfg(test)]
// mod tests {
//     use super::*;

//     macro_rules! longest_common_subsequence_tests {
//         ($($name:ident: $test_case:expr,)*) => {
//             $(
//                 #[test]
//                 fn $name() {
//                     let (first_seq, second_seq, expected_lcs) = $test_case;
//                     assert_eq!(longest_common_subsequence(&first_seq, &second_seq), expected_lcs);
//                 }
//             )*
//         };
//     }

//     longest_common_subsequence_tests! {
//         empty_case: ("", "", ""),
//         one_empty: ("", "abcd", ""),
//         identical_strings: ("abcd", "abcd", "abcd"),
//         completely_different: ("abcd", "efgh", ""),
//         single_character: ("a", "a", "a"),
//         different_length: ("abcd", "abc", "abc"),
//         special_characters: ("$#%&", "#@!%", "#%"),
//         long_strings: ("abcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefgh",
//                       "bcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefgha",
//                       "bcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefghabcdefgh"),
//         unicode_characters: ("你好，世界", "再见，世界", "，世界"),
//         spaces_and_punctuation_0: ("hello, world!", "world, hello!", "hello!"),
//         spaces_and_punctuation_1: ("hello, world!", "world, hello!", "hello!"), // longest_common_subsequence is not symmetric
//         random_case_1: ("abcdef", "xbcxxxe", "bce"),
//         random_case_2: ("xyz", "abc", ""),
//         random_case_3: ("abracadabra", "avadakedavra", "aaadara"),
//     }
// }