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9.6 Implement an algorithm to print all valid (e.g., properly opened and closed) combinations of n-pairs of parentheses.
EXAMPLE
Input: 3
Output: ((())), (()()), (())(), ()(()), ()()()
LeetCode上的原题，请参见我之前的博客Generate Parentheses 生成括号。
解法一：
class Solution { public: vector<string> generateParens(int n) { set<string> t; if (n == 0) t.insert(""); else { vector<string> pre = generateParens(n - 1); for (auto a : pre) { for (int i = 0; i < a.size(); ++i) { if (a[i] == ‘(‘) { a.insert(a.begin() + i + 1, ‘(‘); a.insert(a.begin() + i + 2, ‘)‘); t.insert(a); a.erase(a.begin() + i + 1, a.begin() + i + 3); } } t.insert("()" + a); } } return vector<string>(t.begin(), t.end()); } };
解法二:
class Solution { public: vector<string> generateParens(int n) { vector<string> res; generateParensDFS(n, n, "", res); return res; } void generateParensDFS(int left, int right, string out, vector<string> &res) { if (left > right) return; if (left == 0 && right == 0) res.push_back(out); else { if (left > 0) generateParensDFS(left - 1, right, out + ‘(‘, res); if (right > 0) generateParensDFS(left, right - 1, out + ‘)‘, res); } } };
[CareerCup] 9.6 Generate Parentheses 生成括号
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原文地址：http://www.cnblogs.com/grandyang/p/4828614.html
