[LeetCode] 22. 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:

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

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public class Solution {
    
    public void generateParenthesisAux(int n, int k, int i, char[] path, List res){
        if(0 == k){
            // no more left parenthesis
            for( int l = i; l < n*2; ++l){
                path[l] = ')';
            }
            res.add(new String(path));
            
        }else{
            path[i] = '(';
            generateParenthesisAux(n, k-1, i+1, path, res);
            if((n - k) * 2 > i){
                path[i] = ')';
                generateParenthesisAux(n, k, i+1, path, res);
            }
        }
        
        return;
        
    }
    
    public List generateParenthesis(int n) {
        ArrayList res = new ArrayList();
        generateParenthesisAux(n, n, 0, new char[2*n], res);
        return res;
    }
}