【leetcode】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:

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

 

 

用递归生成所有的括号组合，并且在递归过程中不断剪枝

剪枝的条件：

 leftNum>n||rightNum>n||rightNum>leftNum)

1.左、右括号数目大于了n

2.右括号数目大于了左括号数目

 

 

 1 class Solution {

 2 

 3 public:

 4 

 5     vector<string> generateParenthesis(int n) {

 6 

 7        

 8 

 9         vector<string> result;

10 

11         generate(result,"",0,n,0,0);

12 

13         return result;

14 

15        

16 

17     }

18 

19    

20 

21     void generate(vector<string> &result,string tmp,int index,int &n,int leftNum,int rightNum)

22 

23     {

24 

25         if(leftNum>n||rightNum>n||rightNum>leftNum)

26 

27         {

28 

29             return;

30 

31         }

32 

33         if(index==2*n)

34 

35         {

36 

37             result.push_back(tmp);

38 

39             return;

40 

41         }

42 

43        

44 

45         generate(result,tmp+"(",index+1,n,leftNum+1,rightNum);

46 

47         generate(result,tmp+")",index+1,n,leftNum,rightNum+1);

48 

49     }

50 

51 };