剑指Offer-23合并两个排序的链表

public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    // 伪节点
    ListNode node = new ListNode(-1);
    ListNode head = node;
    ListNode p;
    // 尾插法实现
    while (l1 != null && l2 != null){
        if (l1.val < l2.val){
            p = new ListNode(l1.val);
            l1 = l1.next;
        }else {
            p = new ListNode(l2.val);
            l2 = l2.next;
        }
        node.next = p;
        node = p;
    }
    // 剩余的都接上
    while (l1 != null){
        p = new ListNode(l1.val);
        node.next = p;
        node = p;
        l1 = l1.next;
    }
    while (l2 != null){
        p = new ListNode(l2.val);
        node.next = p;
        node = p;
        l2 = l2.next;
    }
    return head.next;
}

这代码可以简洁很多

public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    // 伪节点
    ListNode head = new ListNode(-1);
    ListNode node = head;
    // 尾插法实现
    while (l1 != null && l2 != null){
        if (l1.val < l2.val){
            node.next = l1;
            l1 = l1.next;
        }else {
            node.next = l2;
            l2 = l2.next;
        }
        node = node.next;
    }
    // 剩余的都接上
    if (l1 != null){
        node.next = l1;
    }
    if (l2 != null){
        node.next = l2;
    }
    return head.next;
}