LeetCode/com/zerroi/leetcode/Three25/RemoveNthFromEnd.java

package com.zerroi.leetcode.Three25;

public class RemoveNthFromEnd {
    public static void main(String[] args) {
//        ListNode head = new ListNode(1, new ListNode(2, new ListNode(3, new ListNode(4, new ListNode(5)))));
        ListNode head = new ListNode(1, new ListNode(2));
        SolutionFirst solutionFirst = new SolutionFirst();
        solutionFirst.removeNthFromEnd(head, 2);
    }
}

class ListNode {
    int val;
    ListNode next;

    ListNode() {
    }

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

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

class SolutionFirst {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        if(head == null) return null;
        ListNode cur = head;
        int length = length(head);
        if(length == 1) return null;
        if (length == n) return head.next;

        ListNode dummy = new ListNode(0, head);
        for (int i = 1; i <= length - n; i++) {
            cur = cur.next;
            dummy = dummy.next;
        }
        dummy.next = cur.next;

        return head;
    }

    private int length(ListNode head) {
        int length = 0;
        while (head != null) {
            length++;
            head = head.next;
        }
        return length;
    }
}