单链表的创建(头插法、尾插法)、插入、删除、查找的代码

单链表是一种线性的数据结构，其中每个节点包含数据和指向下一个节点的指针。以下是单链表的创建（头插法和尾插法）、插入、删除和查找的基本操作。

1. **创建（头插法**）:

// 定义链表节点结构
struct ListNode {
    int val;
    ListNode* next;
    ListNode(int x) : val(x), next(NULL) {}
};

// 使用头插法创建链表
ListNode* createList(vector<int>& nums) {
    if (nums.empty()) return nullptr;
    ListNode* head = new ListNode(nums[0]);
    ListNode* tail = head;
    for (int i = 1; i < nums.size(); ++i) {
        tail->next = new ListNode(nums[i]);
        tail = tail->next;
    }
    return head;
}

2. **创建（尾插法**):

ListNode* tailInsert(ListNode*& head, int val) {
    if (!head) {
        head = new ListNode(val);
        return head;
    }
    ListNode* tail = head;
    while (tail->next) {
        tail = tail->next;
    }
    tail->next = new ListNode(val);
    return head;
}

3. **插入（按值）**:

void insertNode(ListNode* &head, int value, int index) {
    if (index <= 0) {
        ListNode* newNode = new ListNode(value);
        newNode->next = head;
        head = newNode;
    } else {
        ListNode* current = head;
        for (int i = 0; i < index - 1 && current != nullptr; ++i) {
            current = current->next;
        }
        if (current != nullptr) {
            ListNode* newNode = new ListNode(value);
            newNode->next = current->next;
            current->next = newNode;
        }
    }
}

4. **删除**:

void deleteNode(ListNode* &head, int target) {
    if (!head) return;
    if (head->val == target) {
        ListNode* temp = head;
        head = head->next;
        delete temp;
        return;
    }
    ListNode* current = head;
    while (current->next && current->next->val != target) {
        current = current->next;
    }
    if (current->next) {
        ListNode* toDelete = current->next;
        current->next = current->next->next;
        delete toDelete;
    }
}

5. **查找**:

ListNode* searchNode(ListNode* head, int target) {
    ListNode* current = head;
    while (current != nullptr) {
        if (current->val == target) {
            return current;
        }
        current = current->next;
    }
    return nullptr; // 如果未找到，返回nullptr
}