fn remove_symbols(s: &str) -> String {
    return s
        .chars()
        .filter(|&c| c.is_alphanumeric() || c == ' ')
        .collect();
}

fn prime_factors(n: u32) -> Vec<u32> {
    let factors: Vec<u32> = (2..=n).filter(|i| n % i == 0).collect();
    return factors
        .into_iter()
        .take_while(|i| i * i <= n)
        .find(|x| n % x == 0)
        .map(|i| {
            let mut sub_factors = vec![i];
            sub_factors.extend(prime_factors(n / i));
            sub_factors
        })
        .unwrap_or(vec![n])
}

use num::Num;

fn sum<'a, S>(arr: impl IntoIterator<Item = &'a S>) -> S where S: 'a + Num + Copy {
    let mut sum = S::zero();
    for i in arr {
        sum = sum + *i;
    }
    return sum;
}

use std::iter::Sum;

fn sum<T, S>(arr: T) -> S where T: IntoIterator<Item = S>, S: Sum {
    return arr.into_iter().sum();
}

use std::ops::Add;
use num::Zero;

fn sum<T, S>(arr: T) -> S where T: IntoIterator<Item = S>, S: Add<Output = S> + Zero {
    let mut sum: S = Zero::zero();
    for i in arr {
        sum = sum + i;
    }
    return sum;
}

use std::io::*;

fn kashikashi() -> Result<()> {
    const BUFF: [u8; 7] = [104, 101, 108, 108, 111, 10, 55];
    return stdout().write_all(&BUFF);
}

pub fn bool_check(bools: [bool; 3]) -> bool {
    return (bools[0] && bools[1]) || (bools[0] && bools[2]) || (bools[1] && bools[2]);
}

fn math(expression: &str) -> Result<i32, MathError> {
    // remove whitespace
    let expression: String = expression.chars().filter(|ch| !ch.is_whitespace()).collect();
    let operator: char = expression.chars().find(|ch| ['+', '-', '*', '/', '='].contains(&ch)).ok_or(MathError::MissingOperator)?;
    
    // converting each string slice to an integer
    let mut operands = expression.split(operator).filter_map(|n| n.parse::<i32>().ok());
    let num1 = operands.next().ok_or(MathError::InvalidOperand)?;
    let num2 = operands.next().ok_or(MathError::InvalidOperand)?;
    
    // divide by zero check
    if operator == '/' && num2 == 0 {
        return Err(MathError::DivideByZero);
    }
    
    let res: Option<i32> = match operator {
        '+' => num1.checked_add(num2),
        '-' => num1.checked_sub(num2),
        '*' => num1.checked_mul(num2),
        '/' => num1.checked_div(num2),
        '=' => Some((num1 == num2).into()),
        _   => unreachable!()
    };
    
    return res.ok_or(MathError::Overflow);
}

use MathError::*;
#[derive(Debug, PartialEq, Eq)]
enum MathError {
    MissingOperator,
    InvalidOperand,
    DivideByZero,
    Overflow,
}

fn math(expression: &str) -> Result<i32, MathError> {
    // remove whitespace
    let expression: String = expression.chars().filter(|ch| !ch.is_whitespace()).collect();
    let operator: char = expression.chars().find(|ch| ['+', '-', '*', '/', '='].contains(&ch)).ok_or(MathError::MissingOperator)?;
    
    let operands: Vec<i32> = expression.split(operator).filter_map(|n| n.parse().ok()).collect();
    let num1 = *operands.get(0).ok_or(MathError::InvalidOperand)?;
    let num2 = *operands.get(1).ok_or(MathError::InvalidOperand)?;
    
    // check if they divide by zero
    if operator == '/' && num2 == 0 {
        return Err(MathError::DivideByZero);
    }
    
    let res = match operator {
        '+' => num1.checked_add(num2),
        '-' => num1.checked_sub(num2),
        '*' => num1.checked_mul(num2),
        '/' => num1.checked_div(num2),
        '=' => Some((num1 == num2).into()),
        _   => unreachable!()
    };
    
    return res.ok_or(MathError::Overflow);
}

use MathError::*;
#[derive(Debug, PartialEq, Eq)]
enum MathError {
    MissingOperator,
    InvalidOperand,
    DivideByZero,
    Overflow,
}

fn math(expression: &str) -> Result<i32, MathError> {
    // remove whitespace
    let expression: String = expression.chars().filter(|ch| !ch.is_whitespace()).collect();
    let operator: char = expression.chars().find(|ch| ['+', '-', '*', '/', '='].contains(&ch)).ok_or(MathError::MissingOperator)?;
    
    let operands: Vec<i32> = expression.split(operator).filter_map(|n| n.parse().ok()).collect();
    let num1 = *operands.get(0).ok_or(MathError::InvalidOperand)?;
    let num2 = *operands.get(1).ok_or(MathError::InvalidOperand)?;
    
    // check if they divide by zero
    if operator == '/' && num2 == 0 {
        return Err(MathError::DivideByZero);
    }
    
    match operator {
        '+' => num1.checked_add(num2).ok_or(MathError::Overflow),
        '-' => num1.checked_sub(num2).ok_or(MathError::Overflow),
        '*' => num1.checked_mul(num2).ok_or(MathError::Overflow),
        '/' => num1.checked_div(num2).ok_or(MathError::Overflow),
        '=' => Ok((num1 == num2).into()),
        _   => unreachable!()
    }
}

use MathError::*;
#[derive(Debug, PartialEq, Eq)]
enum MathError {
    MissingOperator,
    InvalidOperand,
    DivideByZero,
    Overflow,
}

struct TemperatureConverter {
    // add what you need
}

// implement these three
impl TemperatureConverter {
    fn new(temp: i32) -> Self {
        todo!()
    }
    fn fahrenheit_to_celcius(self) -> f32 {
        todo!()
    }
    fn celsius_to_fahrenheit(self) -> f32 {
        todo!()
    }
}

fn capitalise(s: &str) -> String {
    return s
        .split(' ')
        .map(capitalise_word)
        .collect::<Vec<String>>()
        .join(" ");
}

fn capitalise_word(s: &str) -> String {
    if s.len() == 0 {
        return s.to_uppercase();
    }
    return s.get(0..=0).unwrap().to_uppercase() + s.get(1..).unwrap();
}

fn math(s: &str) -> i32 {
    // first remove whitespace characters so all we have left are digits and the operator
    let num_str: String = s.chars().filter(|ch| *ch != ' ').collect();
    
    // extract the operator character
    let pos: usize = num_str    
        .chars()
        .position(|ch| ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '=')
        .expect("invalid operator, expected '+, -, *, / or =");
    let operator: char = num_str
        .chars()
        .nth(pos)
        .unwrap();
    
    // extract the two numbers from the string
    let num1: i32 = num_str.get(0..pos).unwrap().parse().unwrap();
    let num2: i32 = num_str.get(pos + 1..).unwrap().parse().unwrap();
    
    match operator {
        '+' => num1 + num2,
        '-' => num1 - num2,
        '*' => num1 * num2,
        '/' => num1 / num2,
        _ => (num1 == num2) as i32,
    }
}

fn math(s: &str) -> i32 {
    // first remove whitespace characters so all we have left are digits and the operator
    let num_string: String = s.chars().filter(|ch| *ch != ' ').collect();
    
    // extract the operator character
    let operator: char = num_string
        .chars()
        .find(|ch| ['+', '-', '*', '/', '='].contains(&ch))
        .expect("invalid operator, expected '+, -, *, / or =");
    
    // extract the two numbers from the string
    let num: Vec<i32> = num_string.split(operator).map(|n| n.parse().expect("string contains an invalid number")).collect();
    
    match operator {
        '+' => num[0] + num[1],
        '-' => num[0] - num[1],
        '*' => num[0] * num[1],
        '/' => num[0] / num[1],
        _ => (num[0] == num[1]) as i32,
    }
}