How do you solve Permutation Difference between Two Strings on LeetCode?

Permutation Difference between Two Strings (LeetCode #3146) 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: Using a mapping of indices allows for efficient lookups and calculations.

What is the brute force solution for Permutation Difference between Two Strings?

The brute force approach for Permutation Difference between Two Strings is Brute Force, with O(n²) time complexity and O(1) space complexity. In the brute force approach, we will iterate through each character in the strings and calculate the absolute difference of their indices. This method is straightforward but inefficient for larger strings. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Permutation Difference between Two Strings?

Permutation Difference between Two Strings uses the following concepts: Hash Table, String. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Permutation Difference between Two Strings?

Always clarify the constraints and properties of the input data. Think about how you can optimize a brute force solution and explain your thought process. Practice explaining your code as you write it; this helps in interviews.

What are common mistakes when solving Permutation Difference between Two Strings?

Not considering the uniqueness of characters, leading to incorrect index lookups. Overcomplicating the solution instead of leveraging simple data structures like dictionaries.

#3146

Permutation Difference between Two Strings

Easy

Hash TableStringHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

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Intuition

Time O(n)Space O(n)

In the optimal approach, we will use a single pass to create a mapping of indices for both strings. This allows us to calculate the differences in a more efficient manner, reducing the time complexity.

⚙️

Algorithm

4 steps

1Step 1: Create a dictionary to store the indices of characters in string 's'.
2Step 2: Iterate through string 't' and for each character, find its index in the dictionary for 's'.
3Step 3: Calculate the absolute difference of the indices and accumulate it.
4Step 4: Return the accumulated difference.

solution.py11 lines

1# Full working Python code
2
3def permutation_difference(s, t):
4    index_map = {char: i for i, char in enumerate(s)}
5    difference = 0
6    for i, char in enumerate(t):
7        difference += abs(index_map[char] - i)
8    return difference
9
10# Example usage
11print(permutation_difference('abc', 'bac'))  # Output: 2

ℹ

Complexity note: The time complexity is O(n) because we make a single pass to create the index map and another pass to calculate the differences. The space complexity is O(n) due to the storage of the index map.

1Using a mapping of indices allows for efficient lookups and calculations.
2Understanding the problem constraints (unique characters) simplifies the approach.

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