LeetCode 22. Generate Parentheses分析代码

public class Solution {
    public List<String> generateParenthesis(int n) {
        List<String> res = new ArrayList<>();
        if(n <= 0)
            return res;
        String parent = "";
        dfs(res, "",n , n);
        return res;
    }
    
    private void dfs(List<String> res, String parent, int left, int right) {
        
        if(left == 0 && right == 0) {
            res.add(parent);
            return;
        }
        
        if(left > 0) {
            dfs(res, parent+"(",left-1,right);
        }
        if(right > 0 && right > left) {
            dfs(res, parent + ")",left,right-1);
        }
    }
}