How do you solve Lexicographically Smallest Beautiful String on LeetCode?

Lexicographically Smallest Beautiful String (LeetCode #2663) 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: A beautiful string cannot have palindromic substrings of length 2 or 3.

What is the time complexity of Lexicographically Smallest Beautiful String?

The optimal solution for Lexicographically Smallest Beautiful String runs in O(n) time and uses O(n) space. The complexity is O(n) because we only traverse the string a limited number of times, making it efficient for large inputs.

What is the brute force solution for Lexicographically Smallest Beautiful String?

The brute force approach for Lexicographically Smallest Beautiful String is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves generating all possible strings of length n that are lexicographically larger than s and checking each one to see if it's beautiful. This is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Lexicographically Smallest Beautiful String?

Lexicographically Smallest Beautiful String uses the following concepts: String, Greedy. The recommended patterns to study are: Greedy, Two Pointers, Backtracking.

What are the interview tips for Lexicographically Smallest Beautiful String?

Always clarify the constraints and requirements of the problem before diving into coding. Think about how to efficiently generate or modify strings without brute-force generation. Practice identifying patterns in string manipulation problems, such as palindromes or lexicographical order.

What are common mistakes when solving Lexicographically Smallest Beautiful String?

Failing to check for palindromic conditions after modifying characters. Not considering edge cases where no valid string can be formed.

#2663

Lexicographically Smallest Beautiful String

Hard

StringGreedyGreedyTwo PointersBacktracking

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)

The optimal approach involves modifying the string from the end to the beginning, ensuring that we only change characters when we can maintain the beautiful property. This is more efficient than generating all combinations.

⚙️

Algorithm

5 steps

1Step 1: Convert the string to a character array for easy manipulation.
2Step 2: Iterate from the end of the string to the beginning.
3Step 3: For each character, try to increment it to the next possible character that keeps the string beautiful.
4Step 4: If you can increment, replace the character and fill the rest with the smallest valid characters to ensure the string is beautiful.
5Step 5: If no valid string can be formed, return an empty string.

solution.py14 lines

1# Full working Python code
2
3def next_beautiful_string(s, k):
4    n = len(s)
5    s = list(s)
6    for i in range(n - 1, -1, -1):
7        for c in range(ord(s[i]) + 1, ord('a') + k):
8            s[i] = chr(c)
9            if (i < 1 or s[i] != s[i - 1]) and (i < 2 or s[i] != s[i - 2]):
10                for j in range(i + 1, n):
11                    s[j] = 'a' if s[j - 1] != 'a' else 'b'
12                return ''.join(s)
13            s[i] = chr(ord(s[i]) - 1)  # revert back
14    return ""

ℹ

Complexity note: The complexity is O(n) because we only traverse the string a limited number of times, making it efficient for large inputs.

1A beautiful string cannot have palindromic substrings of length 2 or 3.
2Incrementing characters from the end allows for easier management of the lexicographical order.

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