SHAllenge in Rust

Cargo.toml

[package]
name = "shallenge"
version = "0.1.0"
edition = "2021"

[dependencies]
sha2 = "0.11.0-pre.3"

main.rs

use sha2::{Digest, Sha256};
use std::env;
use std::process::exit;
use std::str;

fn main() {
    let args: Vec<String> = env::args().collect();
    let tmp1 = args[1].clone() + "/";
    let prefix = tmp1.as_bytes();

    let res = &args[2].parse::<i32>();
    if let Err(_e) = res {
        println!("{} is not a number!", &args[2]);
        exit(1);
    }
    let start = res.as_ref().unwrap();

    let res = &args[3].parse::<i32>();
    if let Err(_e) = res {
        println!("{} is not a number!", &args[3]);
        exit(1);
    }
    let end = res.as_ref().unwrap();

    if end <= start {
        println!("end must be greater than start!")
    }

    let mut lowest: [u8; 32] = [255; 32];

    let mut i = start.clone();

    while i < *end {
        let mut hasher = Sha256::new();
        let vec1 = [&prefix[..], &i.to_string().as_bytes()].concat();
        hasher.update(vec1.clone());
        let result = hasher.finalize();
        let hash = result.to_vec();

        if result < lowest.into() {
            let tmp = str::from_utf8(&vec1);
            lowest = result.into();

            println!("{} {}", tmp.unwrap(), hex::encode(&hash));
        }

        i = i + 1;
    }
}