Reverse integer

Math

31.5% acceptance

Jan 12, 2026

15362

13990

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn reverse(x: i32) -> i32 {
    let mut num = x;
    let mut result = 0i32;
    
    while num != 0 {
      let digit = num % 10;
      num /= 10;
      
      // Check for overflow before multiplying by 10
      // If result > i32::MAX / 10, then result * 10 will overflow
      // If result < i32::MIN / 10, then result * 10 will underflow
      if result > i32::MAX / 10 || result < i32::MIN / 10 {
        return 0;
      }
      
      // Check for overflow when adding the digit
      // When result == i32::MAX / 10, we need to ensure that adding digit won't overflow
      // i32::MAX = 2147483647, so i32::MAX / 10 = 214748364
      // When result == 214748364, digit must be <= 7 to not overflow
      // Similarly for negative: i32::MIN = -2147483648, i32::MIN / 10 = -214748364
      // When result == -214748364, digit must be >= -8 to not underflow
      if result == i32::MAX / 10 && digit > 7 {
        return 0;
      }
      if result == i32::MIN / 10 && digit < -8 {
        return 0;
      }
      
      result = result * 10 + digit;
    }
    
    result
  }
}