LeetCode 19 Remove Nth Node From End of list

題目

Given a linked list, remove the nth node from the end of list and return its head.

For example,

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.
Note:
Given n will always be valid.
Try to do this in one pass.

思路

爲這個list定義一個頭指針delNode,而後再定義一個指針指向head,讓這倆指針始終保持n的距離,那delNode.next就是須要刪除的節點,而後刪掉就能夠了,注意特別考慮要刪除的節點是head的狀況,要把head從新指定一下它的位置.

代碼

var removeNthFromEnd = function(head, n) {
    if (head == null) {
        return [];
    }
    var delNode = new ListNode(0);
    delNode.next = head;
    var lastNode = head;
    var dis = 1;
    while (lastNode.next !== null) {
        if (dis < n) {
            lastNode = lastNode.next;
            dis++;
        }
        else {
            delNode = delNode.next;
            lastNode = lastNode.next;
        }      
    }

    var temp = delNode.next;
    delNode.next = temp.next;
    if (temp == head)
        head = delNode.next;
    temp.next = null;
    return head;
    
};