Leetcode 19. 删除链表的倒数第 N 个结点 JavaScript (Day 11)

js一刷自解哈希表

var removeNthFromEnd = function(head, n) {
    let idx=new Map();
    let cur=head;
    while(cur){
        idx.set(cur,1);
        cur=cur.next;
    }
    let keys=[...idx.keys()];
    let temp=keys[keys.length-n];
    if(keys.length-n===0){
        return temp.next;
    }
    let prev=keys[keys.length-n-1];
    prev.next=temp.next;
    return head;



};

js一刷 (哨兵+双指针)

var removeNthFromEnd = function(head, n) {
    let dummy=new ListNode(0,head);
    let left=dummy;
    let right=dummy;
    while(n){
        right=right.next;
        n--;
    }
    while(right.next){
        left=left.next;
        right=right.next;
    }
    let temp=left.next;
    left.next=temp.next;
    return dummy.next;
    
};

哨兵dummy的用法:
有删除头结点的操作的时,用哨兵
当头结点为空,可能返回空结点时,用哨兵