How do you solve Reverse Integer on LeetCode?

Reverse Integer (LeetCode #7) can be solved using Brute Force or Optimal Solution (Mathematical Approach). The optimal approach is Optimal Solution (Mathematical Approach) with O(n) time complexity and O(1) space complexity. Key insight: Recognizing that reversing an integer can be done mathematically without converting to strings is key. This leads to a more efficient solution.

What is the brute force solution for Reverse Integer?

The brute force approach for Reverse Integer is Brute Force, with O(n) time complexity and O(1) space complexity. The brute-force approach involves converting the integer to a string, reversing the string, and then converting it back to an integer. This is straightforward but inefficient for large numbers due to string manipulation. The optimal Optimal Solution (Mathematical Approach) approach improves this to O(n).

What algorithm or data structure is used to solve Reverse Integer?

Reverse Integer uses the following concepts: Math. The recommended patterns to study are: Hash Map, Array, Two Pointers.

What are the interview tips for Reverse Integer?

When you first see this problem, clarify the constraints and ask if you can use 64-bit integers for intermediate calculations. Communicate your approach clearly, explaining why you chose a mathematical method over string manipulation. Mention edge cases such as the smallest and largest 32-bit integers, as well as cases like 0 or numbers with trailing zeros.

What are common mistakes when solving Reverse Integer?

Students often forget to handle negative numbers correctly, leading to incorrect results. Failing to check for overflow before updating the reversed number can result in wrong outputs or exceptions.

Reverse Integer

Medium

MathHash MapArrayTwo Pointers

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Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution (Mathematical Approach)★
Time	O(n)	O(n)
Space	O(1)	O(1)

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Intuition

Time O(n)Space O(1)

Instead of converting to strings, we can reverse the integer mathematically by extracting digits one by one. This is more efficient and avoids the overhead of string manipulation.

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Algorithm

6 steps

1Step 1: Initialize a variable to hold the reversed number (reversed = 0).
2Step 2: While x is not 0, extract the last digit (digit = x % 10).
3Step 3: Update the reversed number (reversed = reversed * 10 + digit).
4Step 4: Check for overflow before updating reversed. If it overflows, return 0.
5Step 5: Remove the last digit from x (x = x // 10).
6Step 6: Continue until x is 0, then return reversed.

solution.py2 lines

1# Full working Python code with comments
2

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Complexity note: The time complexity is O(n) because we are processing each digit of the number once. The space complexity is O(1) since we are using a fixed amount of space regardless of the input size.

1Recognizing that reversing an integer can be done mathematically without converting to strings is key. This leads to a more efficient solution.
2Understanding the importance of checking for overflow at each step can prevent errors and ensure the solution adheres to constraints.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.