61. Rotate List

Problem Statement

Pattern:

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Solution

public ListNode rotateRight (ListNode head, int k){
	// edge case
	if(head == null || head.next == null) return head;
	
	// get last pointer and length of LL
	int len = 1;
	ListNode last = head;
	while(last.next != null) {
		last = last.next;
		len ++;
	}
	last.next = head;   // point last to head
 
	// fix k
	k = k%len;    // set k within bounds
	k = len - k;  // to rotate clockwise
 
	// break LL and return newHead
	while (--k > 0) head = head.next;   // shift head to b4 breakpoint
	ListNode newHead = head.next;       // set newHead
	head.next = null;                   // break LL
	return  newHead;                    // return newHead
}

Notes

• Simple Java Solution - LeetCode Discuss

Steps

1. Make LL Circular
2. Break at k
3. return k.next as new head

Potential Issues:

• K could be much larger than LL Length
• Direction of Rotation needs to be taken into account