leetcode刷题笔记

leetcode22

问题描述：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:[ "((()))","(()())", "(())()", "()(())", "()()()"]

问题分析

该问题是要求输出括号串的数目，本身括号是一种对称结构，所以可以采取回溯的方式来解决，依次输出左右括号，从而保证括号的对称，这里利用了深度优先遍历的思想。具体代码如下：

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

public static void generateParenthesisOneByOne(String sublist,List<String> list,int left,int right){
        if (left > right)
            return;
        if (left>0){
            generateParenthesisOneByOne(sublist+"(",list,left-1,right);
        }
        if (right>0){
            generateParenthesisOneByOne(sublist+")",list,left,right-1);
        }
        if (left == 0 && right == 0)
        {
            list.add(sublist);
            return;
        }
    }

  public static void main(String[] args){
      Scanner scanner = new Scanner(System.in);
      int n = scanner.nextInt();
      List<String> re = generateParenthesis(n);
      for (int i=0;i<re.size();i++){
          System.out.println(re.get(i));
      }
  }