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DeleteMiddleFromTheList.cpp
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DeleteMiddleFromTheList.cpp
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#include <iostream>
using namespace std;
/*
* Delete the Middle Node of a Linked List
You are given the head of a linked list.
Delete the middle node, and return the head of the modified linked list.
The middle node of a linked list of size n is the ⌊n / 2⌋th node from the start using 0-based indexing,
where ⌊x⌋ denotes the largest integer less than or equal to x.
For n = 1, 2, 3, 4, and 5, the middle nodes are 0, 1, 1, 2, and 2, respectively.
Example 1:
Input: head = [1,3,4,7,1,2,6]
Output: [1,3,4,1,2,6]
Explanation:
Since n = 7, node 3 with value 7 is the middle node, which is marked in red.
We return the new list after removing this node.
Example 2:
Input: head = [1,2,3,4]
Output: [1,2,4]
Explanation:
For n = 4, node 2 with value 3 is the middle node, which is marked in red.
Example 3:
Input: head = [2,1]
Output: [2]
Explanation:
The above figure represents the given linked list.
For n = 2, node 1 with value 1 is the middle node, which is marked in red.
Node 0 with value 2 is the only node remaining after removing node 1.
*/
// * Definition for singly-linked list.
struct ListNode
{
int val;
ListNode *next;
ListNode() : val(0), next(nullptr) {}
ListNode(int x) : val(x), next(nullptr) {}
ListNode(int x, ListNode *next) : val(x), next(next) {}
};
class Solution
{
public:
ListNode *deleteMiddle(ListNode *head)
{
if (!head || !head->next)
return NULL; // if 0 or 1 node is present, return NULL
ListNode *prev = NULL, *slow = head, *fast = head; // Maintain 3 Pointers; prev, slow, fast
while (fast and fast->next)
{
prev = slow; // update prev = slow
slow = slow->next; // increment slow once, slow = slow->next;
fast = fast->next->next; // increment fast twice, fast = fast->next->next;
}
prev->next = slow->next; // update connection
delete slow; // deleting middle node
return head; // return head;
}
// Tortoise Method
ListNode *deleteMiddle(ListNode *head)
{
if (!head || !head->next)
return NULL;
// Since we do not access the members within null pointers
ListNode *slow = new ListNode(0);
ListNode *fast = slow;
slow->next = head;
fast->next = head;
// Find the middle of the linked list : Tortoise Method
while (fast->next && fast->next->next)
{
slow = slow->next;
fast = fast->next->next;
}
// Delete a node in a Linked list
slow->next = slow->next->next;
// return the modified Linked list
return head;
}
};