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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;
}
}