Leetcode22. 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:

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

solution:DFS模版

package leetcode2;

import java.util.ArrayList;

public class Generate_parenthese {
public static ArrayList<String> generateParenthesis(int n) {
ArrayList<String> reArrayList=new ArrayList<String>();
String s=new String();
dfs(reArrayList,s,n,n); //DFS的模版递归 dfs(list<E>,E,deep,somethingConstant)
return reArrayList;
}

public static void dfs(ArrayList<String> reArrayList, String s, int left,int right) {
// TODO Auto-generated method stub
// 先考虑deep极值,此处为left，right个数,直接return
if(right<left){
return;
}
if(left==0&&right==0){  //当括号都用完时，将s存入list中
reArrayList.add(s);
return;
}
if(left>0){
dfs(reArrayList, s+'(', left-1, right);
}
if(right>0){
dfs(reArrayList, s+')', left, right-1);
}
}

public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.println(generateParenthesis(3));
}

}