leetcode22:Generate Parentheses

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:

[
  "((()))",
  "(()())",
  "(())()",
  "()(())",
  "()()()"
] 

参考自：http://blog.youkuaiyun.com/yutianzuijin/article/details/13161721

设left为剩下的左括号数，right为剩下的又括号数，当left和right都为0时，结束输出结果，当left>0时可以输出左括号，但是能否输出又括号还得看左括号数和右括号数之间的关系，当left>=right时只能输出左括号，当left<right可以输出右括号。

package leetcode;

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

public class leet22 {
	
	public static void main(String[] args) {
		
		List<String> result = new ArrayList<String>();
		String str = new String();
		
		leet22 leet = new leet22();
		leet.recur(3, 3, str, result);
		System.out.println(Arrays.toString(result.toArray()));
	}
	
	public void recur(int left,int right,String str,List<String> result){
		
		if(left==0&&right==0){
			
			result.add(str);
		}
		if(left>0){
			recur(left-1,right,str+("("),result);
		}
		if(right>0&&left<right){
			recur(left,right-1,str+(")"),result);	
		}
	}
}