|
| 1 | +""" |
| 2 | +author: Aayush Soni |
| 3 | +Given n pairs of parentheses, write a function to generate all |
| 4 | +combinations of well-formed parentheses. |
| 5 | +Input: n = 2 |
| 6 | +Output: ["(())","()()"] |
| 7 | +Leetcode link: https://leetcode.com/problems/generate-parentheses/description/ |
| 8 | +""" |
| 9 | + |
| 10 | + |
| 11 | +def backtrack( |
| 12 | + partial: str, open_count: int, close_count: int, n: int, result: list[str] |
| 13 | +) -> None: |
| 14 | + """ |
| 15 | + Generate valid combinations of balanced parentheses using recursion. |
| 16 | +
|
| 17 | + :param partial: A string representing the current combination. |
| 18 | + :param open_count: An integer representing the count of open parentheses. |
| 19 | + :param close_count: An integer representing the count of close parentheses. |
| 20 | + :param n: An integer representing the total number of pairs. |
| 21 | + :param result: A list to store valid combinations. |
| 22 | + :return: None |
| 23 | +
|
| 24 | + This function uses recursion to explore all possible combinations, |
| 25 | + ensuring that at each step, the parentheses remain balanced. |
| 26 | +
|
| 27 | + Example: |
| 28 | + >>> result = [] |
| 29 | + >>> backtrack("", 0, 0, 2, result) |
| 30 | + >>> result |
| 31 | + ['(())', '()()'] |
| 32 | + """ |
| 33 | + if len(partial) == 2 * n: |
| 34 | + # When the combination is complete, add it to the result. |
| 35 | + result.append(partial) |
| 36 | + return |
| 37 | + |
| 38 | + if open_count < n: |
| 39 | + # If we can add an open parenthesis, do so, and recurse. |
| 40 | + backtrack(partial + "(", open_count + 1, close_count, n, result) |
| 41 | + |
| 42 | + if close_count < open_count: |
| 43 | + # If we can add a close parenthesis (it won't make the combination invalid), |
| 44 | + # do so, and recurse. |
| 45 | + backtrack(partial + ")", open_count, close_count + 1, n, result) |
| 46 | + |
| 47 | + |
| 48 | +def generate_parenthesis(n: int) -> list[str]: |
| 49 | + """ |
| 50 | + Generate valid combinations of balanced parentheses for a given n. |
| 51 | +
|
| 52 | + :param n: An integer representing the number of pairs of parentheses. |
| 53 | + :return: A list of strings with valid combinations. |
| 54 | +
|
| 55 | + This function uses a recursive approach to generate the combinations. |
| 56 | +
|
| 57 | + Time Complexity: O(2^(2n)) - In the worst case, we have 2^(2n) combinations. |
| 58 | + Space Complexity: O(n) - where 'n' is the number of pairs. |
| 59 | +
|
| 60 | + Example 1: |
| 61 | + >>> generate_parenthesis(3) |
| 62 | + ['((()))', '(()())', '(())()', '()(())', '()()()'] |
| 63 | +
|
| 64 | + Example 2: |
| 65 | + >>> generate_parenthesis(1) |
| 66 | + ['()'] |
| 67 | + """ |
| 68 | + |
| 69 | + result: list[str] = [] |
| 70 | + backtrack("", 0, 0, n, result) |
| 71 | + return result |
| 72 | + |
| 73 | + |
| 74 | +if __name__ == "__main__": |
| 75 | + import doctest |
| 76 | + |
| 77 | + doctest.testmod() |
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