_0019RemoveNthNodeFromEndOfList.java

package com.heatwave.leetcode.problems;

/**
 * Given the head of a linked list, remove the nth node from the end of the list and return its head.
 * <p>
 *  
 * <p>
 * Example 1:
 * <p>
 * <p>
 * Input: head = [1,2,3,4,5], n = 2
 * Output: [1,2,3,5]
 * Example 2:
 * <p>
 * Input: head = [1], n = 1
 * Output: []
 * Example 3:
 * <p>
 * Input: head = [1,2], n = 1
 * Output: [1]
 *  
 * <p>
 * Constraints:
 * <p>
 * The number of nodes in the list is sz.
 * 1 <= sz <= 30
 * 0 <= Node.val <= 100
 * 1 <= n <= sz
 * <p>
 * 来源：力扣（LeetCode）
 * 链接：https://leetcode.cn/problems/remove-nth-node-from-end-of-list
 * 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
 */
public class _0019RemoveNthNodeFromEndOfList {
    public static class ListNode {
        int val;
        ListNode next;

        ListNode() {
        }

        ListNode(int val) {
            this.val = val;
        }

        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

    static class Solution {
        public ListNode removeNthFromEnd(ListNode head, int n) {
            ListNode left = head, right = head;

            int count = n + 1;

            while (right != null) {
                right = right.next;
                if (count > 0) {
                    count--;
                } else {
                    left = left.next;
                }
            }

            if (count > 0) {
                return head.next;
            }

            if (left.next != null) {
                left.next = left.next.next;
                return head;
            } else {
                return null;
            }
        }
    }
}