Leetcode刷题Leetcode22

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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));      }  }

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