[CareerCup] 9.6 Generate Parentheses 生成括号

9.6 Implement an algorithm to print all valid (e.g., properly opened and closed) combinations of n-pairs of parentheses.EXAMPLEInput: 3Output: ((())), (()()), (())(), ()(()), ()()()

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 generateParens(int n) {

set t;

if (n == 0) t.insert("");

else {

vector 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(t.begin(), t.end());

}

};

解法二:

class Solution {

public:

vector generateParens(int n) {

vector res;

generateParensDFS(n, n, "", res);

return res;

}

void generateParensDFS(int left, int right, string out, vector &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);

}

}

};

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