707-design-linked-list
Design your implementation of the linked list. You can choose to use a singly or doubly linked list. A node in a singly linked list should have two attributes: val and next. val is the value of the current node, and next is a pointer/reference to the next node. If you want to use the doubly linked list, you will need one more attribute prev to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.
Implement the MyLinkedList class:
MyLinkedList() Initializes the MyLinkedList object. int get(int index) Get the value of the indexth node in the linked list. If the index is invalid, return -1. void addAtHead(int val) Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. void addAtTail(int val) Append a node of value val as the last element of the linked list. void addAtIndex(int index, int val) Add a node of value val before the indexth node in the linked list. If index equals the length of the linked list, the node will be appended to the end of the linked list. If index is greater than the length, the node will not be inserted. void deleteAtIndex(int index) Delete the indexth node in the linked list, if the index is valid.
Example 1:
Input [“MyLinkedList”, “addAtHead”, “addAtTail”, “addAtIndex”, “get”, “deleteAtIndex”, “get”] [[], [1], [3], [1, 2], [1], [1], [1]] Output [null, null, null, null, 2, null, 3]
Explanation MyLinkedList myLinkedList = new MyLinkedList(); myLinkedList.addAtHead(1); myLinkedList.addAtTail(3); myLinkedList.addAtIndex(1, 2); // linked list becomes 1->2->3 myLinkedList.get(1); // return 2 myLinkedList.deleteAtIndex(1); // now the linked list is 1->3 myLinkedList.get(1); // return 3
My solution：
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
84
85
class MyLinkedList(object):
def __init__(self):
self.head = None
self.dummyhead = ListNode(next=self.head)
def get(self, index):
"""
:type index: int
:rtype: int
"""
i = 0
tmp = self.dummyhead
while tmp.next:
if i == index:
break
tmp = tmp.next
i += 1
if i == index and tmp.next:
return tmp.next.val
else:
return -1
def addAtHead(self, val):
"""
:type val: int
:rtype: None
"""
node = ListNode(val=val)
node.next = self.dummyhead.next
self.dummyhead.next = node
def addAtTail(self, val):
"""
:type val: int
:rtype: None
"""
tmp = self.dummyhead
node = ListNode(val = val)
while tmp.next != None:
tmp = tmp.next
tmp.next = node
def addAtIndex(self, index, val):
"""
:type index: int
:type val: int
:rtype: None
"""
i = 0
node = ListNode(val=val)
tmp = self.dummyhead
while tmp.next:
if i == index:
break
tmp = tmp.next
i += 1
if i == index:
node.next = tmp.next
tmp.next = node
def deleteAtIndex(self, index):
"""
:type index: int
:rtype: None
"""
i = 0
tmp = self.dummyhead
while tmp.next:
if i == index:
break
tmp = tmp.next
i += 1
if i == index and tmp.next:
tmp.next = tmp.next.next
# 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)
However, if the indexs of deleteAtIndex() and get() are bigger than the size of the linked list, we will waste a lot of time on counting the size of the linked list. Therefore, using a property named size is useful, and we can modify it when we change the linked list.
Optimize:
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
84
85
86
87
88
89
90
91
92
class MyLinkedList(object):
def __init__(self):
self.dummyhead = ListNode(next=None)
self.size = 0
def get(self, index):
"""
:type index: int
:rtype: int
"""
if index > self.size:
return -1
i = 0
tmp = self.dummyhead
while tmp.next:
if i == index:
break
tmp = tmp.next
i += 1
if i == index and tmp.next:
return tmp.next.val
else:
return -1
def addAtHead(self, val):
"""
:type val: int
:rtype: None
"""
node = ListNode(val=val)
node.next = self.dummyhead.next
self.dummyhead.next = node
self.size += 1
def addAtTail(self, val):
"""
:type val: int
:rtype: None
"""
tmp = self.dummyhead
node = ListNode(val = val)
while tmp.next != None:
tmp = tmp.next
tmp.next = node
self.size += 1
def addAtIndex(self, index, val):
"""
:type index: int
:type val: int
:rtype: None
"""
i = 0
node = ListNode(val=val)
tmp = self.dummyhead
while tmp.next:
if i == index:
break
tmp = tmp.next
i += 1
if i == index:
node.next = tmp.next
tmp.next = node
self.size += 1
def deleteAtIndex(self, index):
"""
:type index: int
:rtype: None
"""
if index > self.size:
return
i = 0
tmp = self.dummyhead
while tmp.next:
if i == index:
break
tmp = tmp.next
i += 1
if i == index and tmp.next:
tmp.next = tmp.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)