LeetCode #22 Generate Parentheses

LeetCode #22 Generate Parentheses

Question

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

[
  "((()))",
  "(()())",
  "(())()",
  "()(())",
  "()()()"
]

Solution

Approach #1

class Solution {
    func generateParenthesis(_ n: Int) -> [String] {
        var results: [String] = []
        func parenthesisStrings(_ str: String, _ open: Int, _ close: Int) {
            if open == 0, close == 0 {
                results.append(str)
                return
            }
            if open > 0 {
                parenthesisStrings(str + "(", open - 1, close)
            }
            if close > open {
                parenthesisStrings(str + ")", open, close - 1)
            }
        }
        parenthesisStrings("", n, n)
        return results
    }
}

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