876. Middle of the Linked List

Problem Statement

Pattern:

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Solution

public static ListNode getMid (ListNode head) {
	ListNode slow = head, fast = head; 
	//fast = fast.next; // increment fast to get floor of mid
	
	while (fast!= null && fast.next!=null) {
		slow = slow.next;
		fast = fast.next.next;
	}
	// when fast / fast.next becomes null, slow would have reached floor of mid
	return slow;
}

Notes

• this question asks for ceil of mid, but if we wanted floor of mid we’de have uncommented fast = fast.next;
• used in merge sorting linked lists : 148. Sort List etc.