22. Generate Parentheses

本文探讨了括号生成问题,即给定一对括号数量n,如何生成所有合法的括号组合。通过递归方法实现了算法,并给出了示例代码及运行结果。适合初学者了解递归算法的应用。

摘要生成于 C知道 ,由 DeepSeek-R1 满血版支持, 前往体验 >

题目描述:

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:感觉应该是要用递归解决,但是不大会写递归的代码....还得练一练。








Discuss:

def generate(p, left, right, parens=[]):
        if left:         generate(p + '(', left-1, right)
        if right > left: generate(p + ')', left, right-1)
        if not right:    parens += p,
        return parens
    return generate('', n, n)

学到:

  1. 递归的写算法题还是很有用的,虽然时间复杂度会很高,有些题确实比较需要,代码看起来会比较简洁。
#include <cassert> /// for assert #include <iostream> /// for I/O operation #include <vector> /// for vector container /** @brief Backtracking algorithms @namespace backtracking / namespace backtracking { /* @brief generate_parentheses class */ class generate_parentheses { private: std::vectorstd::string res; ///< Contains all possible valid patterns void makeStrings(std::string str, int n, int closed, int open); public: std::vectorstd::string generate(int n); }; /** @brief function that adds parenthesis to the string. @param str string build during backtracking @param n number of pairs of parentheses @param closed number of closed parentheses @param open number of open parentheses */ void generate_parentheses::makeStrings(std::string str, int n, int closed, int open) { if (closed > open) // We can never have more closed than open return; if ((str.length() == 2 * n) && (closed != open)) { // closed and open must be the same return; } if (str.length() == 2 * n) { res.push_back(str); return; } makeStrings(str + ')', n, closed + 1, open); makeStrings(str + '(', n, closed, open + 1); } /** @brief wrapper interface @param n number of pairs of parentheses @return all well-formed pattern of parentheses */ std::vectorstd::string generate_parentheses::generate(int n) { backtracking::generate_parentheses::res.clear(); std::string str = “(”; generate_parentheses::makeStrings(str, n, 0, 1); return res; } } // namespace backtracking /** @brief Self-test implementations @returns void */ static void test() { int n = 0; std::vectorstd::string patterns; backtracking::generate_parentheses p; n = 1; patterns = {{“()”}}; assert(p.generate(n) == patterns); n = 3; patterns = {{“()()()”}, {“()(())”}, {“(())()”}, {“(()())”}, {“((()))”}}; assert(p.generate(n) == patterns); n = 4; patterns = {{“()()()()”}, {“()()(())”}, {“()(())()”}, {“()(()())”}, {“()((()))”}, {“(())()()”}, {“(())(())”}, {“(()())()”}, {“(()()())”}, {“(()(()))”}, {“((()))()”}, {“((())())”}, {“((()()))”}, {“(((())))”}}; assert(p.generate(n) == patterns); std::cout << “All tests passed\n”; } /** @brief Main function @returns 0 on exit */ int main() { test(); // run self-test implementations return 0; } 在这段代码的基础上为C++初学者出几个练习题?
最新发布
03-08
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值