Leetcode 22. Generate Parentheses (Medium) (cpp)

Leetcode 22. Generate Parentheses (Medium) (cpp)

Tag: Backtracking, String

Difficulty: Medium

/*

22. Generate Parentheses (Medium)

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:

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

*/
class Solution {
public:
vector<string> generateParenthesis(int n) {
vector<string> res;
string s;
generate(n, n, res, s);
return res;
}
void generate(int p, int q, vector<string>& res, string s) {
if (!p) {
if (q) {
s.push_back(')');
generate(0, q - 1, res, s);
} else {
res.push_back(s);
return;
}
} else if (p == q) {
s.push_back('(');
generate(p - 1, q, res, s);
} else {
s.push_back('(');
generate(p - 1, q, res, s);
s.pop_back();
s.push_back(')');
generate(p, q - 1, res, s);
s.pop_back();
}
}
};