题解 | #合并两个排序的链表#

function ListNode(x){
    this.val = x;
    this.next = null;
}
function Merge(pHead1, pHead2)
{
    // write code here
    //创建新的空链表
    let current = new ListNode();
    //创建哑节点，放置新链表之前，占位(因为current要向前移动，不占位无法找回头指针返回完整链表)
    let dummy = current;
    
    //p1，p2不为空
    while(pHead1 !== null && pHead2 !== null){
        //判断大小
        if(pHead1.val < pHead2.val){
            //将小的节点存入新链表
            current.next = pHead1;
            //并移动p1指针
            pHead1 = pHead1.next;
        }else{
            current.next = pHead2;
            pHead2 = pHead2.next;
        }
        
        //存放完节点，移动新链表指针
        current = current.next;
    }
    
    //当比较完，如果有链表有剩余节点
    if(pHead1 !== null){
        //因为是递增链表，没有比较完的所有节点一定都比新链表大,直接存放
        current.next = pHead1;        
    }
    if(pHead2 !== null){
        current.next = pHead2;        
    }
    //dummy在新链表之前，dummy.next才是完整链表
    return dummy.next;
}
module.exports = {
    Merge : Merge
};