Is Break a Palindrome easy or hard?

Break a Palindrome is classified as a Medium problem on LeetCode. The implementation is short, but identifying the greedy rule—changing the earliest non-'a' character in the left half—requires understanding lexicographic ordering and palindrome symmetry.

Break a Palindrome Python/Java solution

In Python or Java, convert the string to a mutable structure (like a list in Python or a char array in Java). Scan the first half for the first non-'a' character and replace it with 'a'. If none exist, update the last character to 'b'. The implementation runs in O(n) time.

How to solve Break a Palindrome in O(n)?

Iterate through the first half of the palindrome and replace the first character that is not 'a' with 'a'. Because the string is symmetric, modifying one side breaks the palindrome immediately. If all characters are 'a', change the final character to 'b'. This produces the smallest lexicographic result in linear time.

What is the best approach for Break a Palindrome?

The optimal approach is a greedy scan of the first half of the palindrome. Replace the first character that is not 'a' with 'a'. If every character in the first half is already 'a', change the last character to 'b'. This guarantees the lexicographically smallest non-palindrome in O(n) time and O(1) space.

Is Break a Palindrome asked at Google/Amazon/Meta?

Break a Palindrome is a common medium-level string question similar to interview problems asked at companies like Amazon, Google, and Meta. It tests greedy thinking, palindrome properties, and careful handling of edge cases.

What data structure is used in Break a Palindrome?

The problem primarily uses string manipulation with a greedy strategy. No additional data structures are required since the string can be modified directly using character replacement while scanning.

What is the time complexity of Break a Palindrome?

The optimal solution runs in O(n) time because it scans at most half of the string to find a character to modify. Only a constant number of variables are used, so the space complexity is O(1).

Description Hints 4 Solution Video 8:59

1328. Break a Palindrome

Medium51.6% acceptance6 companies

Given a palindromic string of lowercase English letters palindrome, replace exactly one character with any lowercase English letter so that the resulting string is not a palindrome and that it is the lexicographically smallest one possible.

Return the resulting string. If there is no way to replace a character to make it not a palindrome, return an empty string.

A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ, a has a character strictly smaller than the corresponding character in b. For example, "abcc" is lexicographically smaller than "abcd" because the first position they differ is at the fourth character, and 'c' is smaller than 'd'.

Example 1:

Input: palindrome = "abccba"
Output: "aaccba"
Explanation: There are many ways to make "abccba" not a palindrome, such as "zbccba", "aaccba", and "abacba".
Of all the ways, "aaccba" is the lexicographically smallest.

Example 2:

Input: palindrome = "a"
Output: ""
Explanation: There is no way to replace a single character to make "a" not a palindrome, so return an empty string.

Constraints:

1 <= palindrome.length <= 1000
palindrome consists of only lowercase English letters.

Asked at 6 companies

Dell VMware Workday Expedia NVIDIA Mathworks

Topics

Greedy String

Hints open one at a time

Hint 1

How to detect if there is impossible to perform the replacement? Only when the length = 1.

Hint 2

Change the first non 'a' character to 'a'.

Hint 3

What if the string has only 'a'?

Hint 4

Change the last character to 'b'.

8:59

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

Open solution

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1class Solution:
2    def breakPalindrome(self, palindrome: str) -> str:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

"abccba"

Input

"a"

Your code is saved on this device.Solution