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:

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

给定变量n，表示有n对括号，输出n对括号所有正确匹配的情况。

用递归来实现，left和right表示左右括号各剩下多少个，left >= right，即左括号剩下的多，则不能插入右括号。

public class Solution {
    private List<string> result = new List<string>();

    public IList<string> GenerateParenthesis(int n)
    {
        string current = "";
        generate(n, n, current);
        return result;
    }

    public void generate(int left, int right, string current)//left 和 right 表示还剩下的左右括号的个数
    {
        if(left == 0 && right == 0)
        {
            result.Add(current);
            return;
        }
        if(left > 0)
        {
            generate(left - 1, right, current + "(");
        }
        if(right > 0 && left < right)
        {
            generate(left, right - 1, current + ")");
        }
    }
}