0007.Reverse Integer

Link: 7. Reverse Integer - Medium
Track: Amazon Tag

Question

Restate the problem

• Given a signed integer x
• Return its digits reversed
  • if range outside the [-2**31, 2**31 - 1], return 0

While reversing, check for overflow at each step

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Method 1 - Optimal
Method 2

Method 1

Approach

1. Repeatedly take the last digit with num = x % 10
2. Remove the last digit with x //= 10
3. Append the digit to the result with res = res * 10 + num

Complexity

• Time Complexity: O(d)
  • d is the number of digit x
• Space Complexity: O(d)

Edge Case

Code

class Solution:
    def reverse(self, x: int) -> int:
        MAX = 2**31 - 1
        MIN = -2**31
        
        res = 0
        sign = 1 if x > 0 else -1
        x = abs(x)
        while x:
            num = x % 10
            x = x // 10
 
            res = res * 10 + num
            if res < MIN or res > MAX:
                return 0
        
        return sign * res

Method 2

Code

class Solution:
    def reverse(self, x: int) -> int:
        MAX = 2**31 - 1
        MIN = -2**31
        
        sign = 1
        if x < 0:
            sign = -1
            x *= -1
        
        res = int(str(abs(x))[::-1]) * sign
        if res < MIN or res > MAX:
            return 0
 
        return res

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History

• Jan-22-2026 Peeked
  • Integers don’t have a .reverse() method (only lists do).
  • Math way to reverse an integer