Reverse 32-Bit integer

• Reverse the digits of a i32
• If overflow (out of [-2^31, 2^31-1]) return 0
• You can only store int in the 32 bit range

The point:

• Reminder and i32 div
• Edge cases : reversed>INT_MAX//10 (reversed<INT_MAX//10 if neg)

Complexity :

Time	Space
O(1)	O(1)

• O(log(n)) in time because we traverse each digit and the number of digits is around log(n) (log10(n)). We can consider O(1) since i32
• O(1) in space

About Rust :

• Preferred solution?
• YES : tested on the Rust Playground

fn reverse_32_bit_integer(mut n : i32) -> i32{
    let mut reversed_n = 0;

    // keep looping until we've added all digits
    while n != 0 {
        let digit = n % 10;
        n /= 10;
        // if reversed_n > i32::MAX/10 || reversed_n < i32::MIN/10 {
        if !(i32::MIN/10..=i32::MAX/10).contains(&reversed_n) {
            return 0
        }
        reversed_n = reversed_n * 10 + digit;
    }
    reversed_n
}

fn main() { // no main() if this code runs in a Jupyter cell 
    println!("{}", reverse_32_bit_integer(420)); // 24
    println!("{}", reverse_32_bit_integer(-15)); // -51
    println!("{}", reverse_32_bit_integer( 1534236469)); // 0
    println!("{}", reverse_32_bit_integer(-1563847412)); // 0
} // end of local scope OR end of main()

V2

About Rust :

• Hide the compare to i32::MAX and i32::MIN
  • Not sure it’s such a good idea
• YES : tested on the Rust Playground

fn reverse_32_bit_integer(mut n: i32) -> i32 {
    let mut reversed_n : i32 = 0;

    while n != 0 {
        let digit = n % 10;  // Extract the last digit
        n /= 10;             // Remove the last digit from n
        reversed_n = match reversed_n.checked_mul(10).and_then(|v| v.checked_add(digit)) {
            Some(val) => val, // Safe to proceed
            None => return 0, // Overflow detected, return 0 immediately
        };
    }
    reversed_n
}

fn main() { // no main() if this code runs in a Jupyter cell 
    println!("{}", reverse_32_bit_integer(420)); // 24
    println!("{}", reverse_32_bit_integer(-15)); // -51
    println!("{}", reverse_32_bit_integer( 1534236469)); // 0
    println!("{}", reverse_32_bit_integer(-1563847412)); // 0
} // end of local scope OR end of main()