LeetCode in Net

22. Generate Parentheses

Medium

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

Example 1:

Input: n = 3

Output: [”((()))”,”(()())”,”(())()”,”()(())”,”()()()”]

Example 2:

Input: n = 1

Output: [”()”]

Constraints:

• 1 <= n <= 8

Solution

using System.Collections.Generic;
using System.Text;

public class Solution {
    public IList<string> GenerateParenthesis(int n) {
        StringBuilder sb = new StringBuilder();
        List<string> ans = new List<string>();
        return Generate(sb, ans, n, n);
    }

    private IList<string> Generate(StringBuilder sb, List<string> str, int open, int close) {
        if (open == 0 && close == 0) {
            str.Add(sb.ToString());
            return str;
        }
        if (open > 0) {
            sb.Append('(');
            Generate(sb, str, open - 1, close);
            sb.Length--; // Equivalent to deleting the last character in StringBuilder
        }
        if (close > 0 && open < close) {
            sb.Append(')');
            Generate(sb, str, open, close - 1);
            sb.Length--; // Equivalent to deleting the last character in StringBuilder
        }
        return str;
    }
}

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