[LeetCode] 22. 括号生成

时间:2022-08-12 22:20:41

题目链接:https://leetcode-cn.com/problems/generate-parentheses/

题目描述:

给出 n 代表生成括号的对数,请你写出一个函数,使其能够生成所有可能的并且有效的括号组合。

示例:

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

思路:

回溯算法

递归过程中,通过左括号和右括号的个数判断是否还可以组成有效的括号的组合


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代码:

python

class Solution:
def generateParenthesis(self, n: int) -> List[str]:
res = [] def helper(left_p, right_p, tmp):
if left_p == 0 and right_p == 0:
res.append(tmp)
return
if left_p < 0 or right_p < 0 or left_p > right_p:
return
helper(left_p-1, right_p, tmp+"(")
helper(left_p, right_p-1, tmp+")")
helper(n, n, "")
return res

java

class Solution {
public List<String> generateParenthesis(int n) {
ArrayList<String> res = new ArrayList<String>();
backtrack(res, "", n, n);
return res; } public void backtrack(ArrayList<String> res, String s, int left_p, int right_p) {
if (left_p == 0 && right_p == 0) {
res.add(s);
return;
}
if (left_p < 0 || right_p < 0 || left_p > right_p) return;
backtrack(res,s+"(",left_p-1,right_p);
backtrack(res,s+")",left_p,right_p-1);
}
}