anagram_finder.rs

use std::fs::File;
use std::io::{self, prelude::*, BufReader};

const TEST_WORD: &str = "pears"; //The word to check for anagrams of, should be changed to program arguments instead of a constant
const FILE_NAME: &str = "words_alpha.txt"; //A file containing new line delimited words list with alpha characters only
const ALPHABET: &str = "abcdefghijklmnopqrstuvwxyz"; //The English 26 character alphabet
const ALPHABET_SIZE: usize = ALPHABET.len();

const LOOKUP_ORDER: [usize; ALPHABET_SIZE] = [
    //Allows for faster dictionary processing due to the letter frequency of the English language
    2,19,11,9,0,15,16,7,4,22,21,10,13,5,3,18,24,8,6,1,12,20,14,23,17,25
];

const SUMMARY_OFFSET: usize = 'a' as usize;
type WordSummary = [u8; ALPHABET_SIZE];

fn summarise_characters(word: &String) -> WordSummary {
    let mut summary: WordSummary = [0u8; ALPHABET_SIZE];
    for index in word.char_indices() {
        let character: char = index.1;
        if character.is_ascii_lowercase() {
            let mut code_point = character as usize;
            code_point -= SUMMARY_OFFSET;
            code_point = LOOKUP_ORDER[code_point];
            summary[code_point] += 1;
        }
    }
    summary
}
fn summaries_match(a: &WordSummary, b: &WordSummary) -> bool {
    //Relies on the speed of LOOKUP_ORDER
    let mut matched = true;
    for i in 0..ALPHABET_SIZE {
        if a[i] != b[i] {
            matched = false;
            break;
        }
    }
    matched
}

fn main() -> io::Result<()> {
    let file = File::open(FILE_NAME)?;
    let reader = BufReader::new(file);

    let test_word_summary = {
        let test_word = String::from(TEST_WORD);
        let summary = summarise_characters(&test_word);
        summary
    };

    let matches = {
        let mut matches: Vec<String> = Vec::new();
        for line in reader.lines() {
            let word = line?;
            let summary = summarise_characters(&word);
            let is_match = summaries_match(&test_word_summary,&summary);
            if is_match {
                matches.push(word);
            }
        }
        matches
    };

    for word_match in matches {
        println!("{}",word_match);
    }

    Ok(())
}