Is Reverse String Prefix easy or hard?

Reverse String Prefix is considered an Easy problem. The logic involves basic string traversal and a simple prefix reversal using two pointers. It is commonly used to test fundamental string manipulation skills.

Reverse String Prefix Python/Java solution

In Python, you can locate the character using index() and reverse the prefix with slicing like word[:i+1][::-1] + word[i+1:]. In Java, convert the string to a char array and swap characters between index 0 and the target index using two pointers.

How to solve Reverse String Prefix in O(n)?

Scan the string to find the first index of the target character. Once found, place one pointer at the start of the string and another at that index, then swap characters while moving the pointers toward each other. This reverses the prefix in linear time with constant extra space.

What is the best approach for Reverse String Prefix?

The two pointers simulation is the best approach. First locate the index of the target character, then reverse the prefix by swapping characters from both ends until the pointers meet. This solution runs in O(n) time and uses O(1) extra space, making it optimal for interviews.

Is Reverse String Prefix asked at Google/Amazon/Meta?

String manipulation problems like Reverse String Prefix frequently appear in coding interviews at companies such as Amazon, Meta, and Google. While the exact problem may vary, the core skills tested include string processing, pointer manipulation, and clean implementation of simple algorithms.

What data structure is used in Reverse String Prefix?

The optimal solution mainly uses the two pointers technique on a string or character array. Alternative implementations may use a stack to reverse the prefix, but that adds extra space. The in-place two pointer approach avoids additional data structures.

What is the time complexity of Reverse String Prefix?

The time complexity is O(n), where n is the length of the string. You perform a single scan to find the first occurrence of the character and at most another pass to reverse the prefix. Both steps are linear, so the total complexity remains O(n).

Description Hints 1 Solution Video 5:39

3794. Reverse String Prefix

Easy88.5% acceptance1 company

You are given a string s and an integer k.

Reverse the first k characters of s and return the resulting string.

Example 1:

Input: s = "abcd", k = 2

Output: "bacd"

Explanation:

The first k = 2 characters "ab" are reversed to "ba". The final resulting string is "bacd".

Example 2:

Input: s = "xyz", k = 3

Output: "zyx"

Explanation:

The first k = 3 characters "xyz" are reversed to "zyx". The final resulting string is "zyx".

Example 3:

Input: s = "hey", k = 1

Output: "hey"

Explanation:

The first k = 1 character "h" remains unchanged on reversal. The final resulting string is "hey".

Constraints:

1 <= s.length <= 100
s consists of lowercase English letters.
1 <= k <= s.length

Asked at 1 company

Amazon

Topics

String Two Pointers

Hints open one at a time

Hint 1

Simulate as described

5:39

Still stuck?Read the written solution, or watch a walkthrough.

Open solution

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1class Solution:
2    def reversePrefix(self, s: str, k: int) -> str:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

"abcd"
2

Input

"xyz"
3

Input

"hey"
1

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