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

Find the K-th Character in String Game II (LeetCode #3307) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(1) space complexity. Key insight: Understanding how operations affect string length is crucial.

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

The brute force approach for Find the K-th Character in String Game II is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves directly simulating each operation on the string. We keep appending and transforming the string until we reach the desired length, which can be inefficient for large inputs. The optimal Optimal Solution approach improves this to O(n).

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

Find the K-th Character in String Game II uses the following concepts: Math, Bit Manipulation, Recursion. The recommended patterns to study are: Recursion, Dynamic Programming.

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

Always consider the size of the input and whether a brute-force solution is feasible. Think about how to optimize by avoiding unnecessary computations. Practice explaining your thought process clearly, as communication is key in interviews.

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

Students often try to build the entire string instead of tracking lengths. Forgetting to handle character wrapping (e.g., 'z' to 'a').

#3307

Find the K-th Character in String Game II

Hard

MathBit ManipulationRecursionRecursionDynamic Programming

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

💡

Intuition

Time O(n)Space O(1)

Instead of constructing the entire string, we can track the length of the string after each operation. This helps us determine which operation affects the k-th character without building the full string.

⚙️

Algorithm

4 steps

1Step 1: Initialize the length of the string as 1 (for 'a').
2Step 2: Iterate through the operations to calculate the final length of the string after all operations.
3Step 3: Determine which operation affects the k-th character by tracing back through the operations.
4Step 4: Return the character based on the determined operation.

solution.py20 lines

1def findKthCharacter(k, operations):
2    length = 1
3    for op in operations:
4        if op == 0:
5            length *= 2
6        elif op == 1:
7            length *= 2
8    while length > 1:
9        for op in reversed(operations):
10            if op == 0:
11                if k > length // 2:
12                    k -= length // 2
13                length //= 2
14            elif op == 1:
15                if k > length // 2:
16                    k -= length // 2
17                else:
18                    k = (k - 1) % (length // 2) + 1
19                length //= 2
20    return 'a' if k == 1 else 'b'

ℹ

Complexity note: The optimal solution runs in O(n) time because we only iterate through the operations a constant number of times, and we do not build the entire string, just track its length.

1Understanding how operations affect string length is crucial.
2Simulating operations directly can lead to inefficiencies.

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