LeetCode 10.9 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:

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

import java.util.Iterator;import java.util.Stack;public class T5 {public static void main(String[] args) { T5 t=new T5(6); t.DFS(0); t.print(); } Stack<int [] > ans=new Stack<>(); int n; int[] f; int pre=-1; T5(int _n){ n=_n; f=new int[n]; } void DFS(int k){ if(k==n){ int[] arr=new int[n];  for(int i=0;i<n;i++){ arr[i]=f[i]; } ans.add(arr); }else{ for(int i=pre==-1?0:pre;i<n;i++){ if(k<=i){ pre=i; f[k]=i+1; DFS(k+1); } } } } void print(){ int num=1; Iterator<int[]> it = ans.iterator(); while(it.hasNext()){ System.out.println("======"+num+"====="); int []temp=it.next(); String s=""; int l=n; while(l-->0){ s+="("; } for(int i=temp.length-1;i>=0;i--){ s=s.substring(0, temp[i])+")"+s.substring(temp[i]); } System.out.println(s); num++; } }}