leetcode 022 Generate Parentheses

题目

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:

"((()))", "(()())", "(())()", "()(())", "()()()"

思路:

利用递归求解,递归这玩意不好解释,建议调试几次,追踪代码执行过程,用机器的方式去思考。

代码:

private List<String> list;

public List<String> generateParenthesis(int n)
{
    String s = "";
    list = new ArrayList<>();
    generate(n, n, s);
    return list;
}

void generate(int left, int right, String s)
{
    if(left != 0)
    {
        generate(left - 1, right, s + "(");
        if(left != right)
        {
            generate(left, right - 1, s + ")");
        }
    } else
    {
        if(right != 0)
        {
            int tmp = right;
            StringBuilder builder = new StringBuilder(s);
            while(tmp-- > 0)
                builder.append(')');
            list.add(builder.toString());
        }
    }
}

结果细节(图):

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