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Grokking the Coding Interview Patterns in C#

Solution: Permutations

Explore the process of generating all permutations of a string using a recursive subsets pattern approach in C#. Understand how fixing characters and swapping positions systematically produces every possible arrangement. This lesson equips you with efficient methods to solve permutations problems, preparing you for coding interviews.

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Statement

Given an input string, return all possible permutations of the string.

Note: The order of permutations does not matter.

Constraints:

  • All characters in word are unique.

  • 1≤1 \leq word.length ≤6\leq 6

  • All characters in word are lowercase English letters.

Pattern: Subsets

Problems such as this one, where we need to find the combinations or permutations of a given string, are good examples to solve using the subsets pattern as it describes an efficient Depth-First Search (DFS) approach to handle all these problems.

Solution

Let’s discuss a few basics first. We know that n!n! is the number of permutations for a set of size nn. Another obvious and important concept is that if we choose an element for the first position, then the total permutations of the remaining elements are (n−1)!(n-1)!.

For example, if we’re given the string “abcd” and we pick “a” as our first element, then for the remaining elements ...