Leetcode题解（六）

class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        ListNode *helper=new ListNode(0);
        ListNode *head=helper;
        while(l1 && l2)
        {
             if(l1->val<l2->val) helper->next=l1,l1=l1->next;
             else helper->next=l2,l2=l2->next;
             helper=helper->next;
        }
        if(l1) helper->next=l1;
        if(l2) helper->next=l2;
        return head->next;
    }
};

 1 class Solution {
 2 public:
 3     vector<string> generateParenthesis(int n) {
 4         vector<string> res;
 5         string str="";
 6         generateParenthesis(res,n,n,str);
 7 
 8         return res;
 9 
10     }
11     void generateParenthesis(vector<string> &res,int left,int right,string str)
12     {
13         if(0 == left)
14         {
15             for(int i=0;i<right;i++)
16                 str += ‘)‘;
17 
18             res.push_back(str);
19             return;
20         }
21         else
22         {
23             if(left == right)
24                 generateParenthesis(res,left-1,right,str+‘(‘);
25             else
26             {
27                 generateParenthesis(res,left-1,right,str+‘(‘);
28                 generateParenthesis(res,left,right-1,str+‘)‘);
29             }
30         }
31     }
32 };

 1 struct node
 2 {
 3     node(int l,int r,string s)
 4     {
 5         left = l;
 6         right = r;
 7         str = s;
 8     }
 9     int left;
10     int right;
11     string str;
12 };
13  
14 class Solution {
15 public:
16     vector<string> generateParenthesis(int n) {
17         vector<string> res;
18         string str="";
19         stack< node* > mystack;
20         int l = n-1;
21         int r = n;
22 
23         node *temp = new node(l,r,"(");
24         mystack.push(temp);
25         while(!mystack.empty())
26         {
27             temp = mystack.top();
28             mystack.pop();
29             if(temp->left == 0)
30             {
31                 for(int i=0;i<temp->right;i++)
32                     temp->str += ‘)‘;
33                 res.push_back(temp->str);
34                 continue;
35             }
36             if(temp->left == temp->right)
37             {
38                 mystack.push(new node(temp->left -1,temp->right,temp->str+‘(‘));
39             }
40             else
41             {
42                 mystack.push(new node(temp->left -1,temp->right,temp->str+‘(‘));
43                 mystack.push(new node(temp->left,temp->right - 1,temp->str+‘)‘));
44             }
45         }
46         return res;
47 
48     }
49 };