leetcode-22. Generate Parentheses
2016-11-21 14:39
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leetcode-22. Generate Parentheses
题目: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:
[
“((()))”,
“(()())”,
“(())()”,
“()(())”,
“()()()”
]
基本思路就是剩余左括号和右括号的顺序,只要注意右括号不能比做多就行了,虽然标记是回溯法,但是个人觉得用java来写,更像DFS。。毕竟String是final类。。多练练题还是好的,第一次做这题的时候想了很多,刷第二遍leetcode的时候很快就做出来了。
public class Solution { public List<String> generateParenthesis(int n) { List<String> ret = new ArrayList<String>(); helper(ret,n,n,"",n*2); return ret; } private void helper(List<String> ret, int left, int right, String s, int len){ if(s.length()==len){ ret.add(s); return; } if(left > 0){ String s1 = s+"("; helper(ret,left-1,right,s1,len); } if(right>0 && right > left){ String s2 = s+")"; helper(ret,left,right-1,s2,len); } } }
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