Generate Parentheses

22. Generate Parentheses

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:

[
"((()))",
"(()())",
"(())()",
"()(())",
"()()()"
]
class Solution {
func generateParenthesis(_ n: Int) -> [String] {
var result: [String] = []

helper(&result, "", n, n)

return result
}

func helper(_ result: inout [String], _ s: String, _ open: Int, _ close: Int) {
if open == 0 && close == 0 {
result.append(s)
return
}

if open > 0 {
helper(&result, s + "(", open - 1, close)
}
if open < close {
helper(&result, s + ")", open, close - 1)
}
}
}
public class Solution {
public List<String> generateParenthesis(int n) {
List<String> result = new ArrayList<>();
if (n <= 0) {
return result;
}

dfs(result, "", n, n);
return result;
}

void dfs(List<String> result, String s, int left, int right) {
if (left == 0 && right == 0) {
return;
}

if (left > 0) {
dfs(result, s + "(", left - 1, right);
}

if (left < right) {
dfs(result, s + ")", left, right - 1);
}
}
}

Hope this helps,
Michael