22. Generate Parentheses

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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:

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[
 "((()))",
 "(()())",
 "(())()",
 "()(())",
 "()()()"
]

解法1：

比较经典的DFS题目,dfs的思想要掌握
C++

1

Java

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