Q1_middle_of_the_linked_list.cpp

// Given the head of a singly linked list, return the middle node of the linked list.

// If there are two middle nodes, return the second middle node.

// Example 1:
// Input: head = [1,2,3,4,5]
// Output: [3,4,5]
// Explanation: The middle node of the list is node 3.

// Example 2:
// Input: head = [1,2,3,4,5,6]
// Output: [4,5,6]
// Explanation: Since the list has two middle nodes with values 3 and 4, we return the second one.

#include<bits/stdc++.h>
using namespace std;

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) {}
};

// Slow and Fast pointer technique 

class Solution {
public:
    ListNode* middleNode(ListNode* head) {
        ListNode* slow = head;
        ListNode* fast = head;

        while(fast && fast->next) {
            slow = slow->next;
            fast = fast->next->next;
        }
        return slow;
    }
};

// Time Complexity  : O(n/2) = O(n)
// Space Complexity : O(1)