Given a linked list, find its middle element.
If the list has even number of nodes, return the second of the two middle nodes.
{
"head": [1, 2, 3, 4, 5]
}
Output:
3
{
"head": [1, 2, 3, 4]
}
Output:
3
Constraints:
We have provided one solution for this problem.
A naive solution involves computing the length of the list and then traversing exactly half of that.
A faster approach is to use a slow pointer and a fast pointer, with the faster one traversing twice as fast.
By the time the fast one reaches the end of the list, the slower one is at the midpoint. This solution still takes O(n) time but it is faster than the naive one.
O(n).
O(1).
O(n).
/*
* Asymptotic complexity in terms of length of the given linked list \`n\`:
* Time: O(n).
* Auxiliary space: O(1).
* Total space: O(n).
*/
LinkedListNode* find_middle_node(LinkedListNode* head)
{
LinkedListNode *slow_ptr = head;
LinkedListNode *fast_ptr = head;
while (fast_ptr && fast_ptr->next)
{
// Forward two steps.
fast_ptr = fast_ptr->next->next;
// Forward one step.
slow_ptr = slow_ptr->next;
}
return slow_ptr;
}
We hope that these solutions to finding the middle node in a singly linked list problem have helped you level up your coding skills. You can expect problems like these at top tech companies like Amazon and Google.
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