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In this approach, we use a backtracking algorithm to generate all possible letter case permutations for each character in the string. We iterate over each character and decide to either transform it (if it's a letter) or leave it unchanged. By following this approach, we can explore all possible combinations.
Time Complexity: O(2^n), where n is the number of letters in the string.
Space Complexity: O(2^n) for storing the results.
1def backtrack(s, index, path, result):
2 if index == len(s):
3 result.append(''.join(path))
4 return
5 backtrack(s, index + 1, path, result)
6 if s[index].isalpha():
7 path[index] = s[index].swapcase()
8 backtrack(s, index + 1, path, result)
9 path[index] = s[index] # Revert change
10
11
12def letterCasePermutation(S):
13 result = []
14 backtrack(S, 0, list(S), result)
15 return result
16
17
18s = "a1b2"
19permutations = letterCasePermutation(s)
20for perm in permutations:
21 print(perm)
22In Python, the backtracking function explores all permutations by adjusting letter cases and recursively calling itself. A list stores characters of the string, allowing easy swapping. The results are appended to a list which is printed after all possibilities are explored.
This approach utilizes bit manipulation to generate permutations. Each letter can be either in uppercase or lowercase, and we represent each possibility with bits. By iterating through all possible binary combinations (where a bit signifies changing the case of a letter), we construct the result directly.
Time Complexity: O(2^n), where n is the number of letters since we iterate over each possible set of transformations.
Space Complexity: O(2^n) for storage of permutations.
1var letterCasePermutation = function(S) {
This JavaScript solution uses bit manipulation to devise all transformations. It iterates through a binary mask indicating which characters should change case, and appends each result permutation to an array.