LeetCode 022 Generate Parentheses

题目描述：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:

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

 

分析：

递归

 

代码如下：

class Solution {
private:
    vector<string> ret;
public:
    void solve(int dep, int maxDep, int leftNum, int leftNumTotal, string s)
    {
        //如果(个数超出，return
        if (leftNumTotal * 2 > maxDep)
            return;
            
        //如果长度足够，return    
        if (dep == maxDep){
            ret.push_back(s);
            return;
        }
        
        for(int i = 0; i < 2; i++)
        
            //加 (
            if (i == 0)
                solve(dep + 1, maxDep, leftNum + 1, leftNumTotal + 1, s + '(');
            //加 )
            else if (leftNum > 0)
                solve(dep + 1, maxDep, leftNum - 1, leftNumTotal, s + ')');
    }
    
    vector<string> generateParenthesis(int n){
        ret.clear();
        solve(0, 2 * n, 0, 0, "");
        return ret;
    }
};

 Java：

    public List<String> generateParenthesis(int n) {
        
        ArrayList<String> result = new ArrayList<String>();
        dfs(result, "", n, n);
        return result;
        
    }

    public void dfs(ArrayList<String> result, String s, int left, int right) {
        
        if (left > right) {
            return;
        }

        if (left == 0 && right == 0) {
            result.add(s);
            return;
        }

        if (left > 0) {
            dfs(result, s + "(", left - 1, right);
        }

        if (right > 0) {
            dfs(result, s + ")", left, right - 1);
        }

    }