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86 lines
1.7 KiB
Markdown
86 lines
1.7 KiB
Markdown
## Linked List
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<br>
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* each node in a singly-linked list contains a valye and a reference fiedl to link to the next node. the head node (first node) usually represents the whole list.
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* unlike an array, a linked list does not provide constant time access to an index (as it needs to interact through all k elements), however addition and removal of elements are constant time.
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* nodes can be added at the beginning, head needs to be update (`current -> head` and `head = current`).
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* to remove a node you set `prev.next` equal to `node.next`. if it's a double list, you also update `node.next` with `node.next.prev` to `node.prev` (and deallocate the memory).
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<br>
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---
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### detecting cycles
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<br>
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* can be done with hash table or the two-pointer technique, where if there is no cycle, the faster pointer (going 2 steps) will stop at the end of the list, but if there is a cycle, the fast pointer will eventually meet the slow pointer (going 1 step).
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* if there is no cycle, the faster pointer takes `N/2` to reach the end of the list (`N` being the length).
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<br>
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----
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### reversing the list
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<br>
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* keep track of the original head node and the new head node (for instance, with two pointers).
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<br>
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```python
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def reverse_list(head):
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if head is None:
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return head
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final_head = head
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while head.next:
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new_node = head.next
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head.next = new_node.next
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new_node.next = final_head
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final_head = new_node
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return final_head
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```
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<br>
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<br>
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----
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### some exercises in this dir
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<br>
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#### `LinkedListFIFO.py`
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<br>
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```python
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python LinkedListFIFO.py
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Linked List FIFO
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Add 1: None
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Add 2: Nonew
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Add 3: None
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Length: 3
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Find 1: (None, None, 0)
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Delete 1: None
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Length: 0
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Find 1: (None, None, 0)
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```
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<br>
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