题目描述

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:

“((()))”, “(()())”, “(())()”, “()(())”, “()()()”

代码

    public List<String> generateParenthesis(int n) {

        if (n <= 0) {
            return new ArrayList<String>();
        }

        ArrayList<String> result = new ArrayList<String>();
        dfs(result, "", n, n);
        return result;
    }

    void dfs(ArrayList<String> result, String s, int left, int right) {

        if (left > right) {
            return;
        }

        if (left == 0 && right == 0) {
            result.add(s);
        }

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

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