[LeetCode-22] Generate Parentheses

Generate Parentheses

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:

"((()))", "(()())", "(())()", "()(())", "()()()"

 

历遍呢……

 

class Solution {
public:
    vector<string> result;

    bool is_format(const string& str) {
        int left = 0;
        for (int i = 0; i < str.length(); ++i) {
            if ('(' == str[i]) {
                ++left;
            } else if (--left < 0) {
                return false;
            }
        }
        return true;
    }
    
    void append_str(string str, int left, int right) {
        if ((0 == left) && (0 == right) && is_format(str)) {
            result.push_back(str);
            return;
        }
        if (!is_format(str)) {
            return;
        }
        bool is_append = false;
        
        if (left > 0) {
            str.append("(");
            append_str(str, left - 1, right);
            is_append = true;
        }
        if (right > 0) {
            if (is_append) {
                str.erase(str.length() - 1, 1);
            }
            str.append(")");
            append_str(str, left, right - 1);
        }
    }
    
    vector<string> generateParenthesis(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        string str = "";
        result.clear();
        append_str(str, n, n);
        return result;
    }
};