【代码随想录】Day3 203.移除链表元素 707.设计链表 206.反转链表

链表基础知识

链表在内存中不是连续分布的

203.移除链表元素

头节点与非头节点移除方法不一样
运用虚拟头节点来简化代码

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        dummy_head = ListNode( next = head)
        cur = dummy_head
        while cur.next:
            if cur.next.val == val:
                cur.next = cur.next.next
            else:
                cur = cur.next
        return dummy_head.next
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

707.设计链表

class MyLinkedList(object):

    def __init__(self):
        self.dummy_head = ListNode()
        self.size = 0


    def get(self, index):
        """
        :type index: int
        :rtype: int
        """
        if index < 0 or index > self.size:
            return -1
        cur = self.dummy_head.next
        for i in range(index):
            cur = cur.next
        return cur.val
        
    


    def addAtHead(self, val):
        """
        :type val: int
        :rtype: None
        """
        self.dummy_head.next = ListNode(val, self.dummy_head.next)
        self.size +=1
        
    


    def addAtTail(self, val):
        """
        :type val: int
        :rtype: None
        """
        cur = self.dummy_head
        while cur.next:
             cur = cur.next
        cur.next = ListNode(val)
        self.size +=1


    def addAtIndex(self, index, val):
        """
        :type index: int
        :type val: int
        :rtype: None
        """
        if index < 0 or index > self.size:
            return
        cur = self.dummy_head
        for i in range(index):
            cur = cur.next
        cur.next = ListNode(val, cur.next)
        self.size +=1



    def deleteAtIndex(self, index):
        """
        :type index: int
        :rtype: None
        """
        cur = self.dummy_head
        if index < 0 or index > self.size:
            return
        for i in range (index):
            cur = cur.next
        cur.next = cur.next.next
        self.size -=1



# Your MyLinkedList object will be instantiated and called as such:
# obj = MyLinkedList()
# param_1 = obj.get(index)
# obj.addAtHead(val)
# obj.addAtTail(val)
# obj.addAtIndex(index,val)
# obj.deleteAtIndex(index)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83

206.反转链表

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        cur = head
        pre = None
        while cur:
            temp = cur.next
            cur.next = pre
            pre = cur
            cur = temp
        return pre
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19

链表不是很会，明天再复习一下基础知识