题解 | #反转链表#

/*function ListNode(x){
    this.val = x;
    this.next = null;
}*/

// Recursion
function ReverseList(head) {
    if (head === null || head.next === null) return head;
    let res = ReverseList(head.next); 
    head.next.next = head;
    head.next = null;
    return res;
}

// Iteration
function ReverseList(head){
    // write code here
    if (head === null) return head;
    let curr = head;
    let pre = null;
    let next = null;
    while (curr) {
        next = curr.next;
        curr.next = pre;
        pre = curr;
        curr = next;
    }
    head = pre;
    return head;
    
}

module.exports = {
    ReverseList : ReverseList
};