How do you solve Rotate String on LeetCode?

Rotate String (LeetCode #796) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Concatenating the string allows us to check for rotations efficiently.

What is the time complexity of Rotate String?

The optimal solution for Rotate String runs in O(n) time and uses O(n) space. The time complexity is O(n) due to the substring search, and the space complexity is O(n) for the concatenated string.

What is the brute force solution for Rotate String?

The brute force approach for Rotate String is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves generating all possible rotations of the string `s` and checking if any of them match the string `goal`. This is straightforward but inefficient for larger strings. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Rotate String?

Rotate String uses the following concepts: String, String Matching. The recommended patterns to study are: String Matching, Substring Search.

What are the interview tips for Rotate String?

Always consider edge cases, such as different lengths of strings. Think about how to reduce the problem complexity — look for patterns. Practice explaining your thought process clearly as you work through the problem.

What are common mistakes when solving Rotate String?

Not checking if the lengths of `s` and `goal` are equal before proceeding. Overlooking the fact that rotations can be checked using substring search.

#796

Rotate String

Easy

StringString MatchingString MatchingSubstring Search

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

Instead of generating all rotations, we can concatenate the string `s` with itself. If `goal` is a substring of this new string, then `s` can be rotated to form `goal`. This is efficient and avoids unnecessary computations.

⚙️

Algorithm

3 steps

1Step 1: Check if the lengths of `s` and `goal` are equal. If not, return false.
2Step 2: Concatenate `s` with itself to form `s + s`.
3Step 3: Check if `goal` is a substring of `s + s`. If it is, return true; otherwise, return false.

solution.py4 lines

1def rotateString(s, goal):
2    if len(s) != len(goal):
3        return False
4    return goal in (s + s)

ℹ

Complexity note: The time complexity is O(n) due to the substring search, and the space complexity is O(n) for the concatenated string.

1Concatenating the string allows us to check for rotations efficiently.
2The problem can be reduced to a substring search rather than generating all rotations.

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