链表相关题目（持续更新...）

1. 链表反转

题目描述：leetcode-24

function revertList (head) {
    
    
	if(!head)  return null;
	let prev = null, curr = head;
	while(curr) {
    
    
		let next = curr.next;
		prev = curr.next;
		curr = next;
	}
	return prev;
}

2.合并两个有序链表

题目描述：leetcode-21

1. 递归

var mergeTwoLists = function(l1, l2) {
    
    
    if (l1 === null) {
    
    
        return l2;
    } else if (l2 === null) {
    
    
        return l1;
    } else if (l1.val < l2.val) {
    
    
        l1.next = mergeTwoLists(l1.next, l2);
        return l1;
    } else {
    
    
        l2.next = mergeTwoLists(l1, l2.next);
        return l2;
    }
};

2. 迭代

function mergeList (l1, l2) {
    
    
	const preNode = new ListNode(-1);
	const pre = preNode;
	while(l1 !==null && l2!==null){
    
    
		if(l1.val <ls.val) {
    
    
			pre.next = l1;
			l1 = l1.next;
		} else {
    
    
			pre.next = l2;
			l2 = l2.next;
		}
		pre = pre.next;
	}
	 // 合并后 l1 和 l2 最多只有一个还未被合并完，我们直接将链表末尾指向未合并完的链表即可
	 pre.next = l1===null ? l2 : l1;
	return preNode.next;
 }