diff --git a/linked_lists/README.md b/linked_lists/README.md index 51ddc66..89ada1f 100644 --- a/linked_lists/README.md +++ b/linked_lists/README.md @@ -2,22 +2,69 @@
-* unlike an array, a 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. +* 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. + +* 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. + +* nodes can be added at the beginning, head needs to be update (`current -> head` and `head = current`). + * 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).
+ +--- + ### detecting cycles
-* 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). if there is no cycle, the faster pointer takes `N/2` to reach the end of the list (`N` being the length). +* 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). + +* if there is no cycle, the faster pointer takes `N/2` to reach the end of the list (`N` being the length).
---- -### `LinkedListFIFO.py` +### reversing the list + +
+ +* keep track of the original head node and the new head node (for instance, with two pointers). + +
+ +```python +def reverse_list(head): + + if head is None: + return head + + final_head = head + + while head.next: + + new_node = head.next + head.next = new_node.next + new_node.next = final_head + final_head = new_node + + return final_head +``` + + +
+ +
+ +---- + +### some exercises in this dir + +
+ +#### `LinkedListFIFO.py`