int n1 = l1 ? l1->val: 0;

This code initializes an integer variable n1 with the value of l1->val if l1 is not null, otherwise it sets n1 to 0. Here, l1 is presumably a pointer to a node in a linked list, and l1->val is the value stored in that node.

The ternary operator "?" is used to check if l1 is not null. If it is not null, then n1 is set to l1->val, otherwise it is set to 0. This is a shorthand way of writing an if-else statement.

Overall, this code is a simple way to handle null values in a linked list without having to write an if-else statement explicitly.

相关问题

int n1 = l1 ? l1->val : 0; 是 啥意思

这行代码是一个三目运算符，可以理解为以下的if-else语句：

int n1;
if (l1 != NULL) {
    n1 = l1->val;
} else {
    n1 = 0;
}

如果 `l1` 不为空指针，则将 `l1` 节点的值赋给 `n1`，否则将 `n1` 赋为0。

#include <iostream> using namespace std; struct ListNode { int val; ListNode* next; ListNode(int x) : val(x), next(NULL) { }}; class LinkedList { public: static ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) { ListNode dummy(0); ListNode* tail = &dummy; while (l1 && l2) { if (l1->val < l2->val) { tail->next = l1; l1 = l1->next; } else { tail->next = l2; l2 = l2->next; } tail = tail->next; } tail->next = l1 ? l1 : l2; return dummy.next; } }; int main() { ListNode* l1 = nullptr; ListNode* l2 = nullptr; int n1, n2; cin >> n1 >> n2; for (int i = 0; i < n1; i++) { int x; cin >> x; ListNode* node = new ListNode(x); if (l1 == nullptr) { l1 = node; } else { ListNode* cur = l1; while (cur->next) { cur = cur->next; } cur->next = node; } } for (int i = 0; i < n2; i++) { int x; cin >> x; ListNode* node = new ListNode(x); if (l2 == nullptr) { l2 = node; } else { ListNode* cur = l2; while (cur->next) { cur = cur->next; } cur->next = node; } } ListNode* mergedList = LinkedList::mergeTwoLists(l1, l2); while (mergedList) { cout << mergedList->val << " "; mergedList = mergedList->next; } cout << endl; return 0; }详细解释每一句代码

下面是每行代码的详细解释：

#include <iostream>
using namespace std;

包含iostream头文件，并使用命名空间std。

struct ListNode {
    int val;
    ListNode* next;
    ListNode(int x) : val(x), next(NULL) { }
};

定义链表节点结构体ListNode，每个节点包含一个整型数值val和一个指向下一个节点的指针next。构造函数初始化节点的val值为传入的参数x，next指针初始化为NULL。

class LinkedList {
public:
    static ListNode* mergeTwoLists(ListNode* l1, ListNode* l2)
    {
        ListNode dummy(0);
        ListNode* tail = &dummy;
        while (l1 && l2)
        {
            if (l1->val < l2->val)
            {
                tail->next = l1;
                l1 = l1->next;
            }
            else
            {
                tail->next = l2;
                l2 = l2->next;
            }
            tail = tail->next;
        }
        tail->next = l1 ? l1 : l2;
        return dummy.next;
    }
};

定义一个LinkedList类，其中包含一个静态方法mergeTwoLists用于合并两个有序链表。参数l1和l2分别为要合并的两个链表的头节点指针。函数中创建一个虚拟头节点dummy，用于方便后续的链表合并操作。通过tail指针来表示合并后的链表的最后一个节点，根据l1和l2当前节点值的大小关系来更新tail指向的节点。最后将剩余未合并的链表接到tail后面，返回合并后链表的头节点指针。

int main() {
    ListNode* l1 = nullptr;
    ListNode* l2 = nullptr;
    int n1, n2;
    cin >> n1 >> n2;
    for (int i = 0; i < n1; i++)
    {
        int x;
        cin >> x;
        ListNode* node = new ListNode(x);
        if (l1 == nullptr)
        {
            l1 = node;
        }
        else
        {
            ListNode* cur = l1;
            while (cur->next)
            {
                cur = cur->next;
            }
            cur->next = node;
        }
    }
    for (int i = 0; i < n2; i++)
    {
        int x;
        cin >> x;
        ListNode* node = new ListNode(x);
        if (l2 == nullptr)
        {
            l2 = node;
        }
        else
        {
            ListNode* cur = l2;
            while (cur->next)
            {
                cur = cur->next;
            }
            cur->next = node;
        }
    }
    ListNode* mergedList = LinkedList::mergeTwoLists(l1, l2);
    while (mergedList)
    {
        cout << mergedList->val << " ";
        mergedList = mergedList->next;
    }
    cout << endl;
    return 0;
}

主函数中首先定义了两个链表的头节点指针l1和l2以及两个整型变量n1和n2，分别表示两个链表的节点个数。通过输入流cin读取参数n1和n2以及链表节点的值，并创建相应的节点。对于第一个链表l1，在链表为空的情况下将第一个节点赋值为头节点，否则遍历链表直到找到最后一个节点将新节点插入。对于第二个链表l2同理。接着调用LinkedList::mergeTwoLists方法将两个链表合并，并遍历输出合并后链表的每个节点的值。最后输出一个换行符并返回0表示程序运行正常结束。