GenerateParentheses.java

package leetcode;

import java.util.ArrayList;
import java.util.List;

/**
 * @author eko
 * @date 2018/10/21 8:04 PM
 *
 * 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:
 *
 * [
 *   "((()))",
 *   "(()())",
 *   "(())()",
 *   "()(())",
 *   "()()()"
 * ]
 */
public class GenerateParentheses {
    public static void main(String[] args) {
        List<String> res = new GenerateParentheses().generateParenthesis(3);
        System.out.println(res);
    }

    public List<String> generateParenthesis(int n) {
        List<String> list = new ArrayList<String>();
        backtrack(list, "", 0, 0, n);
        return list;
    }

    public void backtrack(List<String> list, String str, int open, int close, int max){

        if(str.length() == max*2){
            list.add(str);
            return;
        }

        if(open < max)
            backtrack(list, str+"(", open+1, close, max);
        if(close < open)
            backtrack(list, str+")", open, close+1, max);
    }
}