n0007_reverse_integer.rs

/**
 * [7] Reverse Integer
 *
 * Given a 32-bit signed integer, reverse digits of an integer.
 * 
 * Example 1:
 * 
 * 
 * Input: 123
 * Output: 321
 * 
 * 
 * Example 2:
 * 
 * 
 * Input: -123
 * Output: -321
 * 
 * 
 * Example 3:
 * 
 * 
 * Input: 120
 * Output: 21
 * 
 * 
 * Note:<br />
 * Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [-2^31,  2^31 - 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.
 * 
 */
pub struct Solution {}

// submission codes start here
impl Solution {
    pub fn reverse(x: i32) -> i32 {
        let mut input: i64 = x as i64;
        let mut result: i64 = 0;
        let mut digit: i64 = 0;
        let base: i64 = 2;
        let upper_bound: i64 = base.pow(31) - 1;
        let lower_bound: i64 = - base.pow(31);
        while input != 0 {
            digit = input % 10;
            result = result * 10 + digit;
            input = input / 10;
        }
        if result > upper_bound || result < lower_bound {
            return 0;
        }
        result as i32
    }
}

// submission codes end

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_7() {
        assert_eq!(Solution::reverse(123), 321);
        assert_eq!(Solution::reverse(-123), -321);
        assert_eq!(Solution::reverse(0), 0);
        assert_eq!(Solution::reverse(-123000), -321);
        let base: i64 = 2;
        assert_eq!(Solution::reverse((base.pow(31) - 1) as i32), 0);
        assert_eq!(Solution::reverse((-base.pow(31)) as i32), 0);
    }
}