leetcode / 算法
  a few seconds read (About 109 words) 0 visits

problem

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

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For example, given n = 3, a solution set is:

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

approach1

深度优先搜索

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class Solution {
    public List<String> generateParenthesis(int n) {
        List<String> res = new ArrayList<>();
        helper(res, "", n, 0, 0);
        return res;

    }

    private void helper(List<String> res, String s, int n, int left, int right) {
        if (right == n) {
            res.add(s);
            return;
        }

        if (left < n) {
            helper(res, s + "(", n, left + 1, right);
        }
        if (right < left) {
            helper(res, s + ")", n, left, right + 1);
        }
    }
}
  • time:O(n!) O(2^n) 卡特兰数
  • space:O(n)
  DFS, backtracking
32.N皇后问题：leetcode51
29.二叉树的最小深度:leetcode111

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