Leetcode 22-24

No. 22 Generate Parentheses （重点）

Solution: DFS

直接代码：

 1 class Solution:
 2     def generateParenthesis(self, n: int) -> List[str]:
 3         if not n:
 4             return []
 5         
 6         left, right, out = n, n, []
 7         self.dfs(left, right, out, "")
 8         return out
 9     
10     def dfs(self, left, right, out, string):
11         if right < left:
12             return
13         if not left and not right:
14             out.append(string)
15             return
16         if left:
17             self.dfs(left-1, right, out, string + "(")
18         if right:
19             self.dfs(left, right-1, out, string + ")")

No. 23 Merge k Sorted Lists （HARD）

 

No. 24 Swap Nodes in Pairs

Solution:

方法一：Iteratively

 1 class Solution:
 2     def swapPairs(self, head: ListNode) -> ListNode:
 3         if not head:
 4             return None
 5         
 6         out = pre = ListNode(None)
 7         pre.next = head
 8         
 9         while head and head.next:
10             temp = head.next.next
11             pre.next = head.next
12             pre.next.next = head
13             head.next = temp
14             
15             pre = pre.next.next
16             head = pre.next
17         
18         return out.next

 

方法二： Recursively

1 class Solution:
2     def swapPairs(self, head: ListNode) -> ListNode:
3         if head and head.next:
4             temp = head.next
5             head.next = self.swapPairs(temp.next)
6             temp.next = head
7             return temp
8         return head

 

posted @ 2019-06-04 14:53  ArthurH  阅读(163)  评论(0)  编辑  收藏  举报