链表算法之【删除链表的倒数第n个节点】

目录

LeetCode-19题

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LeetCode-19题

给定一个链表的头节点，删除链表的倒数第n个节点，并返回删除后的头节点

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        // check
        if (head == null || n <= 0) {
            return head;
        }
        // 双指针
        ListNode dummyHead = new ListNode(0, head);
        ListNode p1 = dummyHead;
        ListNode p2 = dummyHead;
        for (int i = 0; i < n; i++) {
            p2 = p2.next;
        }
        while (p2 != null && p2.next != null) {
            p2 = p2.next;
            p1 = p1.next;
        }
        // 此时删除的就是链表倒数第n个节点
        p1.next = p1.next.next;
        return dummyHead.next;
    }

    private static class ListNode {
        int val;
        ListNode next;

        public ListNode() {
        }

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

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