Longest Palindromic Substring in Rust

Welcome to the Longest Palindromic Substring 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;

fn usage() -> ! {
    println!("Usage: please provide a string that contains at least one palindrome");
    exit(0);
}

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

// Find longest palindromic string using matching array
// Source: https://www.geeksforgeeks.org/longest-palindromic-substring-using-dynamic-programming/
fn longest_palindromic_substring(s: &str) -> String {
    // Initialize array indicating whether there is a character match
    // between two characters to indicate that nothing matches
    let n = s.len();
    let mut matches: Matrix<bool> = vec![vec![false; n]; n];

    // Indicate all length 1 strings match
    for i in 0..n {
        matches[i][i] = true;
    }

    // Convert string to a lowercase vector of characters
    let chars: Vec<char> = s
        .to_lowercase()
        .chars()
        .collect();

    // Find all length 2 matches
    let mut start = 0;
    let mut max_len = 1;
    for i in 0..(n - 1) {
        if chars[i] == chars[i + 1] {
            matches[i][i + 1] = true;
            start = i;
            max_len = 2;
        }
    }

    // Find all length 3 or higher matches
    for len in 3..=n {
        // Loop through each starting character
        for i in 0..(n - len + 1) {
            // If match for one character in from start and end characters
            // and start and end characters match, set match for start and
            // end characters, and update max length
            let j = i + len - 1;
            if matches[i + 1][j - 1] && chars[i] == chars[j] {
                matches[i][j] = true;
                if len > max_len {
                    start = i;
                    max_len = len;
                }
            }
        }
    }

    chars[start..start + max_len]
        .iter()
        .collect()
}

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

    // Exit if 1st command-line argument is empty
    let s: &str = &args
        .next()
        .unwrap_or_else(|| usage());
    if s.len() < 1 {
        usage();
    }

    // Get longest palindromic substring. Error if none found
    let longest = longest_palindromic_substring(s);
    if longest.len() < 2 {
        usage();
    }

    // Show longest palindromic substring
    println!("{longest}");
}

Longest Palindromic Substring 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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