DS-002 28 数据结构：链表及代码实现

Code Implementation of Link list

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1 Construction of link list

1.1 Construct a link list

typedef struct Link{
    char elem; 				// Represents the data field
    struct Link * next; 	// Represents the pointer field, point to the subsequent element
}link; 						// link is the name of the node (every node is a 'link' struct

1.2 Initialize the link list

Here we introduce two ways to initialize the link list, we can use a list with a head node or without a head node. Assume that we need to store “1,2,3,4” in the link list, here two ways.

Without a head node:

link * initLink(){
    link * p=NULL;									// Create the head pointer
    link * temp = (link*)malloc(sizeof(link));		// Create the first node
    temp->elem = 1;									// Initialize the first pointer
    temp->next = NULL;
    p = temp;										// The head pointer point to the first node
    for (int i=2; i<5; i++) {
        link *a=(link*)malloc(sizeof(link));		// Create and initialize each node
        a->elem=i;
        a->next=NULL;
        temp->next=a;								// Construct connection
        temp=temp->next;							// Move the pointer
    }
    return p;										// Return the head pointer
}

With a head node:

link * initLink1(){
    link * p=(link*)malloc(sizeof(link));			// Create a head node
    link * temp=p;									// A pointer point to the head node   									
    for (int i=1; i<5; i++) {						// Create the link list
        link *a=(link*)malloc(sizeof(link));
        a->elem=i;
        a->next=NULL;
        temp->next=a;
        temp=temp->next;
    }
    return p;
}

1.3 Display the link list

Now let’s try to display the link list:

void display(link *p){		// Without head node
    link* temp=p;			// Pointer 'temp' point to the head node
    while (temp) {    
        printf("%d ",temp->elem);
        temp=temp->next;
    }
    printf("\n");
} 

However, if the link list has a head node, the code should be sightly changed as follows:

void display1(link *p){		// With head node
    link* temp=p;
    while (temp->next) {
        temp=temp->next;
       	printf("%d ",temp->elem);
    }
    printf("\n");
}

Here’s the main function:

int main() {
    printf("The initialized link list：\n");
    link *p=initLink();
    link *q=initLink1();
    display(p);
    display1(q);
    return 0;
}

Output:

We can see that the results are the same.

2 Basic operations of link list

2.1 Insert elements

// p:original link list，elem:new elements，add:inserted position
link * insertElem(link * p,int elem,int add){
    link * temp=p;							// Create temperary node
    for (int i=1; i<add; i++) {				// Find the last node before the inserted place
        if (temp==NULL) {
            printf("Invalid position\n");
            return p;
        }
        temp=temp->next;
    }   
    link * c=(link*)malloc(sizeof(link));	// Create the inserted node 'c'
    c->elem=elem;
    c->next=temp->next;						// Insert the node
    temp->next=c;
    return  p;
}

2.2 Delete elements

//p:original link list, add:the value of the element to be deleted
link * delElem(link * p,int add){
    link * temp=p;
    for (int i=1; i<add; i++) {	    // 'temp' points to the last node before the deleted node
        temp=temp->next;
    }
    link * del=temp->next;			// Set a pointer point to the deleted node
    temp->next=temp->next->next;	// Change the pointer
    free(del);						// Free the node
    return p;
}

2.3 Find the element

//p:original link，elem:the value of the target
int selectElem(link * p,int elem){
    link * t=p;					// Create new pointer 't' and initialized as head pointer 'p'
    int i=1;
    while (t->next) {		
        t=t->next;
        if (t->elem==elem) {
            return i;
        }
        i++;
    }
    return -1;					// Failed to find the target
}

2.4 Alter the element

//add: position, newElem: the value of the new data field
link *amendElem(link * p,int add,int newElem){
    link * temp=p;
    temp=temp->next;				// Before the traversal, 'temp' points to the first node
    for (int i=1; i<add; i++) {		// Traverse to the node to be deleted
        temp=temp->next;
    }
    temp->elem=newElem;
    return p;
}

2.5 Check the code

int main() {
    printf("Initialize the link list：\n");
    link *p=initLink();
    display(p);
  
    printf("Insert 5 at position 4：\n");
    p=insertElem(p, 5, 4);
    display(p);
  
    printf("Delete element 3:\n");
    p=delElem(p, 3);
    display(p);
  
    printf("Find the element 2：\n");
    int address=selectElem(p, 2);
    if (address==-1) {
        printf("Element not found");
    }else{
        printf("The position of element 2 is：%d\n",address);
    }
    printf("Change the element at position 3 for 7:\n");
    p=amendElem(p, 3, 7);
    display(p);
  
    return 0;
}

Output: