Is Reverse String easy or hard?

Reverse String is classified as an easy problem. The logic is straightforward once you recognize the symmetric swap pattern, making it a common warm-up problem for practicing arrays, strings, and the two-pointer technique.

How to solve Reverse String in O(n)?

Use two pointers that start at opposite ends of the character array. Swap the characters at the pointers, then move them inward until they meet. This performs the reversal in linear time O(n) and constant space O(1) without allocating a new string.

Reverse String Python or Java solution?

In Python, swap characters using two indices inside a loop while left < right. In Java, use a char array and perform in-place swaps with a temporary variable. Both implementations follow the same two-pointer logic and run in O(n) time with O(1) extra space.

What is the best approach for Reverse String?

The two-pointer approach is the most efficient method. Start with one pointer at the beginning and another at the end of the array, swap the characters, and move both pointers toward the center. This completes the reversal in O(n) time and O(1) space since the operation is done in-place.

What data structure is used in Reverse String?

The problem operates directly on a character array, which behaves like a mutable string structure. The algorithm relies on index-based access and swaps, combined with the two-pointer technique for efficient traversal from both ends.

What is the time complexity of Reverse String?

The optimal solution runs in O(n) time because each character is processed at most once. In the two-pointer approach, roughly n/2 swaps occur. Recursive implementations also take O(n) time but use additional stack space.

Is Reverse String asked at Google, Amazon, or Meta?

Reverse String is a common introductory string manipulation problem that appears in coding interviews and screening rounds at companies like Amazon and Meta. It is often used to test understanding of in-place array operations and the two-pointer technique.

Description Hints 1 Solution Video 9:03

344. Reverse String

Q: What is the best approach for Reverse String?

The two-pointer approach is the most efficient method. Start with one pointer at the beginning and another at the end of the array, swap the characters, and move both pointers toward the center. This completes the reversal in O(n) time and O(1) space since the operation is done in-place.

Q: What data structure is used in Reverse String?

The problem operates directly on a character array, which behaves like a mutable string structure. The algorithm relies on index-based access and swaps, combined with the two-pointer technique for efficient traversal from both ends.

Q: What is the time complexity of Reverse String?

The optimal solution runs in O(n) time because each character is processed at most once. In the two-pointer approach, roughly n/2 swaps occur. Recursive implementations also take O(n) time but use additional stack space.

Q: Is Reverse String asked at Google, Amazon, or Meta?

Reverse String is a common introductory string manipulation problem that appears in coding interviews and screening rounds at companies like Amazon and Meta. It is often used to test understanding of in-place array operations and the two-pointer technique.

Easy81.2% acceptance16 companies

Write a function that reverses a string. The input string is given as an array of characters s.

You must do this by modifying the input array in-place with O(1) extra memory.

Example 1:

Input: s = ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]

Example 2:

Input: s = ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]

Constraints:

1 <= s.length <= 10⁵
s[i] is a printable ascii character.

Asked at 16 companies

Qualcomm Microsoft

TCS EPAM Systems Siemens Wipro HCLTech

Google Amazon Bloomberg Apple

Infosys

+4 more

Meta Accenture NVIDIA Goldman Sachs

Topics

String Two Pointers

Hints open one at a time

Hint 1

The entire logic for reversing a string is based on using the opposite directional two-pointer approach!

9:03

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution