How do you solve Find the K-th Character in String Game I on LeetCode?

Find the K-th Character in String Game I (LeetCode #3304) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(log n) time complexity and O(1) space complexity. Key insight: Understanding the exponential growth of the string helps in optimizing the solution.

What is the time complexity of Find the K-th Character in String Game I?

The optimal solution for Find the K-th Character in String Game I runs in O(log n) time and uses O(1) space. The optimal solution runs in O(log n) time because we are effectively halving the length of the string in each iteration, making it very efficient.

What is the brute force solution for Find the K-th Character in String Game I?

The brute force approach for Find the K-th Character in String Game I is Brute Force, with O(n²) time complexity and O(1) space complexity. We can simulate the string generation process by repeatedly applying the transformation until the string length reaches at least k. This approach is straightforward but inefficient for larger values of k. The optimal Optimal Solution approach improves this to O(log n).

What algorithm or data structure is used to solve Find the K-th Character in String Game I?

Find the K-th Character in String Game I uses the following concepts: Math, Bit Manipulation, Recursion, Simulation. The recommended patterns to study are: Exponential Growth, Backtracking.

What are the interview tips for Find the K-th Character in String Game I?

Always think about the constraints and whether a brute force solution is feasible. Look for patterns in the problem that can simplify your approach. Practice explaining your thought process clearly as you code.

What are common mistakes when solving Find the K-th Character in String Game I?

Students often try to build the entire string instead of recognizing the pattern. Forgetting to adjust the index when returning the k-th character.

#3304

Find the K-th Character in String Game I

Easy

MathBit ManipulationRecursionSimulationExponential GrowthBacktracking

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(log n)
Space	O(1)	O(1)

💡

Intuition

Time O(log n)Space O(1)

Instead of generating the entire string, we can determine the k-th character by understanding the pattern of how characters evolve. Each character's position can be traced back to the original 'a' without constructing the full string.

⚙️

Algorithm

4 steps

1Step 1: Initialize the current length of the string as 1 (for 'a').
2Step 2: Calculate the length of the string after each transformation until it exceeds k.
3Step 3: Determine which segment the k-th character falls into by backtracking through the transformations.
4Step 4: Calculate the character based on its position in the original string.

solution.py11 lines

1def findKthCharacter(k):
2    length = 1
3    current = 'a'
4    while length < k:
5        length *= 2
6        current = chr(ord(current) + 1)
7    while length > 1:
8        length //= 2
9        if k > length:
10            k -= length
11    return current

ℹ

Complexity note: The optimal solution runs in O(log n) time because we are effectively halving the length of the string in each iteration, making it very efficient.

1Understanding the exponential growth of the string helps in optimizing the solution.
2Backtracking through the transformations allows us to find the k-th character without full string construction.

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