Is Lexicographically Smallest String After Reverse II easy or hard?

The problem is considered Hard because it combines string transformations with efficient lexicographic comparison. A naive solution is simple to write but too slow, while the optimized solution requires knowledge of rolling hash, binary search, or suffix array techniques.

Lexicographically Smallest String After Reverse II Python/Java solution

Most implementations follow the same structure across languages: compute prefix hashes, iterate over candidate reversal ranges, and compare results using binary search and substring hash checks. Python, Java, and C++ versions differ mainly in hash handling and modular arithmetic.

What is the best approach for Lexicographically Smallest String After Reverse II?

The most practical approach uses rolling hash with binary search to compare candidate strings. Precompute prefix hashes so substring comparisons take O(1). For each possible reversal, use binary search to find the first differing position between candidates. This reduces overall complexity to about O(n log n).

Is Lexicographically Smallest String After Reverse II asked at Google/Amazon/Meta?

String optimization problems involving lexicographic order, substring reversal, and hashing are common in interviews at companies like Google, Amazon, and Meta. Variants often test rolling hash, suffix arrays, or efficient substring comparison techniques.

What data structure is used in Lexicographically Smallest String After Reverse II?

Typical solutions rely on rolling hash arrays for fast substring hashing, along with binary search for prefix comparison. Some advanced implementations also use suffix arrays and LCP structures to perform lexicographic comparisons efficiently.

What is the time complexity of Lexicographically Smallest String After Reverse II?

The optimized solution using rolling hash and binary search runs in O(n log n) time with O(n) space. Brute force solutions that rebuild and compare strings require O(n^3) time because there are O(n^2) reversals and each comparison may scan the entire string.

Description Hints 1

3735. Lexicographically Smallest String After Reverse II

Q: How to solve Lexicographically Smallest String After Reverse II in O(n log n)?

Precompute polynomial rolling hashes for the string and its reversed version. For each possible substring reversal, simulate the candidate string logically instead of building it. Use binary search to find the longest common prefix between two candidates and compare the next character using hash queries. This keeps each comparison to O(log n).

Hard49.0% acceptancePremium elsewhere, free here

You are given a string s of length n consisting of lowercase English letters.

You must perform exactly one operation by choosing any integer k such that 1 <= k <= n and either:

reverse the first k characters of s, or
reverse the last k characters of s.

Return the lexicographically smallest string that can be obtained after exactly one such operation.

Example 1:

Input: s = "dcab"

Output: "acdb"

Explanation:

Choose k = 3, reverse the first 3 characters.
Reverse "dca" to "acd", resulting string s = "acdb", which is the lexicographically smallest string achievable.

Example 2:

Input: s = "abba"

Output: "aabb"

Explanation:

Choose k = 3, reverse the last 3 characters.
Reverse "bba" to "abb", so the resulting string is "aabb", which is the lexicographically smallest string achievable.

Example 3:

Input: s = "zxy"

Output: "xzy"

Explanation:

Choose k = 2, reverse the first 2 characters.
Reverse "zx" to "xz", so the resulting string is "xzy", which is the lexicographically smallest string achievable.

Constraints:

1 <= n == s.length <= 10⁵
s consists of lowercase English letters.

Topics

Hints open one at a time

Hint 1

Use binary search and hashing for faster lexicographically smaller comparisons

LanguageLoading editor…

1class Solution:
  def solve(self):
      pass


Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

"dcab"

Input

"abba"

Input

"zxy"

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