发生冲突后在哈希表中实现链接时出现分段错误

Question

我正在尝试实现链接（哈希表中的冲突解决技术）。我的程序适用于大多数测试用例。

这是我的程序（它很大，但我知道它失败的地方。所以你可以跳过这部分，如果你想。）：

#include<stdio.h>
#include<stdlib.h>

struct LinkedListNode
{
    int data;
    struct LinkedListNode *next;
};

struct LinkedListNode* getNewNode()
{
    // I don't need to cast the malloc in c
    return malloc(sizeof(struct LinkedListNode));
}

struct LinkedListNode* insertAtBeginning(struct LinkedListNode** hashTable, int index, int data)
{
    struct LinkedListNode* newNode = getNewNode(); // the new node
    newNode->data = data;
    newNode->next = NULL; // for now I can put the next to be null

    // check if the block is containing null or not
    if (hashTable[index] == NULL)
    {
        // now just insert the new element at beginning
        hashTable[index] = newNode;
        return hashTable[index]; // returning the new address of the block
    }

    // if collisions occur
    struct LinkedListNode* blockListAddress = hashTable[index]; // the address pointing to first node of linked list
    newNode->next = blockListAddress; // storing the address of block in the next of the new linkedlist
    hashTable[index] = newNode; // changing the block address to the address of new node (as we have to insert in beginning)
    return hashTable[index];
}

struct LinkedListNode* searchMe(struct LinkedListNode** hashTable, int index, int key)
{
    struct LinkedListNode* res = NULL;
    struct LinkedListNode* temp = hashTable[index];

    if (temp == NULL)
        return NULL;

    // if we just have one element in the block then the while loop below won't get executed
    // because here condition is temp->next which will be null, thus here I have written if condition
    if (hashTable[index] != NULL && hashTable[index]->data == key)
    {
        return hashTable[index];
    }

    // if not null then traverse through linked list
    while (temp != NULL)
    {
        printf("
TEMP = %d", temp);
        if (key == temp->data)
            res = temp;
        printf("
temp->data=%d
", temp->data);
        temp = temp->next;
    }
    return res;
}

int hashFunction(int num)
{
    return num%10;
}

int main()
{
    int n;
    printf("
Enter elements to be stored
");
    scanf("%d", &n);

    // declaring the hashTable of size n (i.e. size of input elements), its gonna have pointers to LinkedListNode
    struct LinkedListNode** hashTable = malloc(n*sizeof(struct LinkedListNode*)); // I have given memory to the table, now I even need to give memory to the elements in the table
    int i;
    for (i = 0; i < n; ++i)
    {
        hashTable[i] = NULL;
    }

    int d;
    printf("
Enter the elements in array
");
    for (i = 0; i < n; ++i)
    {
        scanf("%d", &d);
        int hashedValue = hashFunction(d);
        hashTable[hashedValue] = insertAtBeginning(hashTable, hashedValue, d);
    }

    int key;
    printf("
Enter the element you want to search for
");
    scanf("%d", &key);
    int ind = hashFunction(key);
    struct LinkedListNode* res = searchMe(hashTable, ind, key);

    if (res == NULL)
    {
        printf("
Not found
");
    }
    else
    {
        printf("
%d is found
", res->data);
    }
}


// time complexity in worst case for searching = O(n),
// average case t.c = O(1+alpha), where alpha = n/m
// n <- number of elements in hashtable
// m <- size of hashtable
// so alpha is 1 in this case
// thus average t.c = theta(1)

该程序为此测试用例提供SIGSEGV：

输入要存储的元素

5

输入数组中的元素

21 32 565 784 445

输入要搜索的元素

565

TEMP = 35383520

TEMP->数据= 445

TEMP = 35383456

TEMP->数据= 565

分段故障（核心转储）

经过调试后，我发现它在第56行引发了seg故障，即：

if (key == temp->data)

这一行写在以下代码片段中：

while (temp != NULL)
{
    printf("
TEMP = %d", temp);
    if (key == temp->data)
        res = temp;
    printf("
temp->data=%d
", temp->data);
    temp = temp->next;
}

正如您在上面的失败测试中所看到的那样，while循环执行了3次（它应该只执行两次，因为temp应该第三次指向null）。虽然它正在执行第三次，但它在if (key == temp->data)线上抛出了段错误。

这意味着temp不是NULL，它甚至没有data字段。所以在插入时可能存在问题（即插入newNode的下一个字段可能不会被制作为NULL，但我正在妥善处理那个事情。）如果插入时会出现问题，那么我的代码应该失败其他测试用例。但代码只是失败了上面的指定测试用例。

例如，代码通过了这个测试用例：

[aupadhyay @ localhost c] $ ./a.out

输入要存储的元素

7

输入数组中的元素

21 32 565 784 445 655 84

输入要搜索的元素

565

TEMP = 8063248

TEMP->数据= 655

TEMP = 8063216

TEMP->数据= 445

TEMP = 8063152

TEMP->数据= 565

找到565

我只是无法弄明白，为什么它没有提到上述测试用例。

Answer 1

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