Classic Interview 150 Questions P61 Rotate List

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Timeline

Timeline

2025-11-21

init

linked list

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Problem:

P61 Rotate List

https://leetcode.cn/problems/rotate-list/description/?envType=study-plan-v2&envId=top-interview-150

Split the linked list into two groups, then attach the tail of the latter group to the front group.

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 *rotateRight(ListNode *head, int k)
	{
		int nr_node = 0;
		ListNode *p = head, *new_head_prev, *new_head, *tail;

		while (p != nullptr) {
			if (p->next == nullptr) {
				tail = p;
			}
			p = p->next;
			nr_node++;
		}
		if (nr_node == 0) { // in case divided by zero
			return head;
		}
		k = k % nr_node;
		if (k == 0) { // head == nullptr || k==0
			return head;
		}
		new_head_prev = head;
		for (int i = 0; i < nr_node - k - 1; i++) {
			new_head_prev = new_head_prev->next;
		}
		new_head = new_head_prev->next;
		tail->next = head;
		new_head_prev->next = nullptr;
		return new_head;
	}
};