GenerateParentheses.java

package com.leetcode;

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

/**
 * Created by jamylu on 2018/1/7.
 * leetcode022.
 * Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
 */
public class GenerateParentheses {
    public static void main(String[] args) {
        int n = 3;
        System.out.println(generate(n));
    }

    //回溯法
    public static List<String> generate(int n) {
        List<String> ans = new ArrayList<>();
        backtrack(ans, "", 0, 0, n);
        return ans;
    }

    public static void backtrack(List<String> ans, String cur, int open, int close, int max) {
        if (cur.length() == max * 2) {
            ans.add(cur);
            return;
        }

        if (open < max) {
            backtrack(ans, cur + "(", open + 1, close, max);
        }
        if (close < open) {
            backtrack(ans, cur + ")", open, close + 1, max);
        }
    }
}