Longest Common Subsequence in Rust

Welcome to the Longest Common Subsequence in Rust page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

use std::env::args;
use std::process::exit;
use std::str::FromStr;

fn usage() -> ! {
    println!("Usage: please provide two lists in the format \"1, 2, 3, 4, 5\"");
    exit(0);
}

fn parse_int<T: FromStr>(s: &str) -> Result<T, <T as FromStr>::Err> {
    s.trim().parse::<T>()
}

fn parse_int_list<T: FromStr>(s: &str) -> Result<Vec<T>, <T as FromStr>::Err> {
    s.split(',')
        .map(parse_int)
        .collect::<Result<Vec<T>, <T as FromStr>::Err>>()
}

type Matrix<T> = Vec<Vec<T>>;

// Longest Common Sequence
// Source: https://en.wikipedia.org/wiki/Longest_common_subsequence#Example_in_C#
//
// However, instead of storing lengths, an index to the subsequence is stored
fn longest_common_subsequence<T>(list1: &Vec<T>, list2: &Vec<T>) -> Vec<T> 
where
    T: Copy + Clone + PartialEq
{
    // Initialize all subsequences to an empty sequence
    let m = list1.len();
    let n = list2.len();
    let mut c: Matrix<usize> = vec![vec![0; n + 1]; m + 1];
    let mut subsequences: Matrix<T> = vec![vec![]];

    // Find the longest common subsequence using prior subsequences
    for i in 1..=m {
        for j in 1..=n {
            // If common element found, create new subsequence based on prior
            // subsequence with the common element appended
            if list1[i - 1] == list2[j - 1] {
                c[i][j] = subsequences.len();
                let mut new_subsequence = subsequences[c[i - 1][j - 1]].clone();
                new_subsequence.push(list1[i - 1]);
                subsequences.push(new_subsequence);
            }
            // Else, reuse the longer of the two prior subsequences
            else {
                let index1 = c[i][j - 1];
                let index2 = c[i - 1][j];
                c[i][j] = if subsequences[index1].len() > subsequences[index2].len() {
                    index1
                }
                else {
                    index2
                }
            }
        }
    }

    subsequences[c[m][n]].clone()
}

fn main() {
    let mut args = args().skip(1);

    // Convert 1st command-line argument to list of integers
    let list1: Vec<i32> = args
        .next()
        .and_then(|s| parse_int_list(&s).ok())
        .unwrap_or_else(|| usage());

    // Convert 2nd command-line argument to list of integers
    let list2: Vec<i32> = args
        .next()
        .and_then(|s| parse_int_list(&s).ok())
        .unwrap_or_else(|| usage());

    // Get longest common subsequence and display it
    let result: Vec<i32> = longest_common_subsequence::<i32>(&list1, &list2);
    println!("{result:?}");
}

Longest Common Subsequence in Rust was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

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