Practical Guide to Linked Lists & Dynamic Memory Management

1. LISTS Pointers Singly Linked Lists Dynamically Linked Stacks and Queues Polynomials Additional List Operations Equivalence List Operations Sparse Matrices Doubly Linked Lists

2. 연결리스트 배열 : 저장방법 오버플로우 삽입,삭제  데이터의 이동 35삽입 10삭제

3. 연결리스트 연결리스트 : 삽입, 삭제가 용이 노드 : 데이터_필드 링크_필드 데이터 이동 불필요, 포인터 변경

4. 10 20 50 Ù node 포인터(Pointers) • linked representation of ordered lists • successive items of a list may be placed anywhere in memory. • associated with each list element is a node which contains both a data component and a pointer, called link, to the next item in the list ptr

5. Dynamically Allocated Storage • malloc and free /* <alloc.h> */ int i, *pi; float f, *pf; pi = (int *) malloc(sizeof(int)); pf = (float *) malloc(sizeof(float)); *pi = 1024; *pf = 3.14; printf(“n integer = %d, a float = %f\n”, *pi, *pf); free(pi); free(pf);

6. Singly linked lists • Linked lists representation (1) the nodes do not reside in sequential locations (2) the locations of the nodes may change on different runs ptr bat cat sat vat NULL

7. (ex) Insertion and Deletion in linked lists ptr bat cat sat vat NULL mat ptr bat cat mat sat vat NULL

8. Creation of a list Declaration typedef struct list_node *list_pointer;typedef struct list_node { char data [4]; list_pointer link; }; Creation list_pointer ptr =NULL; Testing#define IS_EMPTY(ptr) (!(ptr)) Allocationptr=(list_pointer) malloc (sizeof(list_node)); struct node{ char data[4]; struct node *link;}; typedef struct node list_node;typedef list_node *list_pointer; • self-referential structure • create a pointer to a type that does not get exist • NULL: defined in stdio.h(K&RC) or stddef.h(ANSI C)

9. #include <stdio.h> struct node { int data; struct node *link; }; typedef struct node list_node; typedef list_node *list_pointer; void main(void) { list_pointer a; a = (list_pointer) malloc(sizeof(list_node)); a->data = 10; printf("%d \n", a->data); }

10. ptr 10  20 NULL list_pointer create2( ){/* create a linked list with two nodes */ list_pointer first, second; first = (list_pointer) malloc(sizeof(list_node)); second = ( list_pointer) malloc(sizeof(list_node)); second -> link = NULL; second -> data = 20; first -> data = 10; first ->link = second; return first;}

11. int i, *pi; 2000 1000 pi ? ? i pi = &i; 2000 1000 i pi ? 1000 *pi i = 10 or *pi = 10 2000 1000 i pi 10 1000 *pi

12. typedef struct list_node *list_pointer; typedef struct list_node { int data; list_pointer link; }; list_pointer ptr = NULL; 1000 ptr NULL ptr->data(*ptr).data ptr = malloc(sizeof(list_node)); 2000 *ptr 1000 ptr 2000 data link

13. (ex) Insertion (1) Two node list (2) Insert a new node temp after a node node : insert(&ptr, node) ptr 10 20 NULL ptr 10 20 NULL node 50 temp

14. void insert(list_pointer *ptr, list_pointer node) { /* insert a new node with data =50 into the list ptr after node */ list_pointer temp; temp = (list_pointer) malloc(sizeof(list_node)); if (IS_FULL(temp)) { fprintf(stderr, “The memory is full \n”); exit(1); } temp->data = 50; if (*ptr) { temp->link = node->link; node->link = temp; } else { temp->link = NULL; *ptr = temp; } }

15. 10 50 20 NULL 50 20 NULL 10 50 20 NULL 10 20 NULL (ex) Deletion • delete(ptr, trail, node) : delete node from the list ptr, where trail points to the node that precedes node (1) delete(&ptr, NULL, ptr) ptr node trail = NULL ptr (a) before deletion (b) after deletion (2) delete(&ptr, ptr, ptr->link) ptr trail node ptr (a) before deletion (b) after deletion

16. void delete (list_pointer *ptr, list_pointer trail, list_pointer node) { /*delete node form the list, trail is the preceding node ptr is the the head of the list */ if (trail) trail->link = node->link; else *ptr = (*ptr)->link; free(node); }

17. 다항식(Polynomials) • Representing polynomials as linked lists typedef struct poly_node *poly_pointer typedef struct poly_node { int coef; int expon; poly_pointer link; } poly_pointer a, b, d; coef expon link

18. a = 3x14 + 2x8 + 1 b = 8x14 - 3x10 + 10x6 a 3 14 2 8 1 0 Ù b 8 14 -3 10 10 6 Ù

19. poly_pointer padd(poly_pointer a, poly_pointer b) { poly_pointer front, rear, temp; int sum; rear =(poly_pointer)malloc(sizeof(poly_node)); if ( IS_FULL(rear) ) { fprintf(stderr, “The memory is full\n”); exit(1); } front = rear; while (a && b) { switch (COMPARE(a->expon, b->expon)) { case -1: /* a->expon < b->expon */ attach(b->coef, b->expon, &rear); b= b->link; break;

20. case 0: /* a->expon == b->expon */ sum = a->coef + b->coef; if (sum) attach(sum,a->expon,&rear); a = a->link; b = b->link; break; case 1: /* a->expon > b->expon */ attach(a->coef, a->expon, &rear); a = a->link; } } for (; a; a = a->link) attach(a->coef, a->expon, &rear); for (; b; b=b->link) attach(b->coef, b->expon, &rear); rear->link = NULL; temp = front; front = front->link; free(temp); return front; }

21. 3 14 2 8 1 0 ptr 원형리스트(Circular list) • Representing polynomials as circularly linked lists • We can free all the nodes more efficiently if we modify our list structure so that the link field of the last node points to the first node in the list, called circular list. • A singly linked list in which the last node has a null link is called a chain. • Erase a circular list in a fixed amount of time

22. Head Node • Circular link for an empty list => head node a Zero polynomials 3 14 2 8 1 0 a 3x14 + 2x8 + 1

23. Additional list operations • Operations for chains • inverting a chain : invert() • concatenate two chains : concatenate()

24. struct node { int data; struct node *link; }; typedef struct node list_node; typedef list_node *list_pointer; 연결리스트의 역순화 void invert(list_pointer *grocery) { list_pointer *p, *q, *r; p = grocery; q = NULL: while(p != NULL) { r = q; q = p; p = p -> link; q -> link = r; } grocery = q; }

25. struct node { int data; struct node *link; }; typedef struct node list_node; typedef list_node *list_pointer; 두 연결리스트의 접합 void concat(grocery, vegetable, x) { list_pointer *temp; if (grocery == NULL) x = vegetable; else { x = grocery; if (vegetable !=NUL) { temp = x; while (temp->link!=NULL) temp = temp -> link; temp -> link = vegetable; } } }

26. Additional list operations Operations for circulary linked lists • Suppose we insert a new node at the front of the list since we have to change the link field of the last node, we must move down to the last node. • More convenient if the name of the circular list points to the last node rather than the first.

27. (ex) Circular list with the name pointing to the last node (a) point to the first node • Insertion of a node at the front or at the rear of a circular list takes a fixed amount of time. x1 x2 xn ptr (b) point to the last node x1 x2 xn ptr

28. Sparse Matrices inadequacies of sequential schemes (1) # of nonzero terms will vary after some matrix computation (2) matrix just represents intermediate results new scheme Each column (row): a circular linked list with a head node

29. down head right next row col down entry right value Revisit Sparse Matrices # of head nodes = max{# of rows, # of columns} head node entry node entry j i aij aij

30. Linked Representation for Matrix 4 4 0 2 11 1 1 1 0 12 5 1 2 -4 3 3 -15 Circular linked list

31. #define MAX_SIZE 50 /* size of largest matrix */typedef enum {head, entry} tagfield;typedef struct matrix_node *matrix_pointer;typedef struct entry_node { int row; int col; int value; };typedef struct matrix_node { matrix_pointer down; matrix_pointer right; tagfield tag; union { matrix_pointer next; entry_node entry; } u; };matrix_pointer hdnode[MAX_SIZE];

32. *Figure 4.22: Sample input for sparse matrix (p.174)

33. Read in a Matrix matrix_pointer mread(void) { /* read in a matrix and set up its linked list. An global array hdnode is used */ int num_rows, num_cols, num_terms; int num_heads, i; int row, col, value, current_row; matrix_pointer temp, last, node; printf(“Enter the number of rows, columns and number of nonzero terms: “);

34. scanf(“%d%d%d”, &num_rows, &num_cols, &num_terms); num_heads = (num_cols>num_rows)? num_cols : num_rows; /* set up head node for the list of head nodes */ node = new_node(); node->tag = entry; node->u.entry.row = num_rows; node->u.entry.col = num_cols; if (!num_heads) node->right = node; else { /* initialize the head nodes */ for (i=0; i<num_heads; i++) { term= new_node(); hdnode[i] = temp; hdnode[i]->tag = head; hdnode[i]->right = temp; hdnode[i]->u.next = temp; } O(max(n,m))

35. current_row= 0; last= hdnode[0]; for (i=0; i<num_terms; i++) { printf(“Enter row, column and value:”); scanf(“%d%d%d”, &row, &col, &value); if (row>current_row) { last->right= hdnode[current_row]; current_row= row; last=hdnode[row]; } temp = new_node(); temp->tag=entry; temp->u.entry.row=row; temp->u.entry.col = col; temp->u.entry.value = value; last->right = temp;/*link to row list */ last= temp; /* link to column list */ hdnode[col]->u.next->down = temp; hdnode[col]=>u.next = temp; }

36. /*close last row */ last->right = hdnode[current_row]; /* close all column lists */ for (i=0; i<num_cols; i++) hdnode[i]->u.next->down = hdnode[i]; /* link all head nodes together */ for (i=0; i<num_heads-1; i++) hdnode[i]->u.next = hdnode[i+1]; hdnode[num_heads-1]->u.next= node; node->right = hdnode[0]; } return node; } O(max{#_rows, #_cols}+#_terms)

37. Write out a Matrix void mwrite(matrix_pointer node) { /* print out the matrix in row major form */ int i; matrix_pointer temp, head = node->right; printf(“\n num_rows = %d, num_cols= %d\n”, node->u.entry.row,node->u.entry.col); printf(“The matrix by row, column, and value:\n\n”); for (i=0; i<node->u.entry.row; i++) { for (temp=head->right;temp!=head;temp=temp->right) printf(“%5d%5d%5d\n”, temp->u.entry.row, temp->u.entry.col, temp->u.entry.value); head= head->u.next; /* next row */ } }

38. Erase a Matrix void merase(matrix_pointer *node) { int i, num_heads; matrix_pointer x, y, head = (*node)->right; for(i=0; i<(*node)->u.entry.row; i++) { y=head->right; while (y!=head) { x = y; y = y->right; free(x); } x= head; head= head->u.next; free(x); } y = head; while (y!=*node) { x = y; y = y->u.next; free(x); } free(*node); *node = NULL; } O(#_rows+#_cols+#_terms)

39. Doubly Linked Lists • We can move easily only in the direction of the links in singly linked list. • To move in either direction, it is useful to have doubly linked lists. typedef struct node *node_pointer; typedef struct node { node_pointer llink; element item; node_pointer rlink; } ptr = ptr->llink->rlink = ptr->rlink->llink

40. (ex) Doubly linked circular list llink item rlink Head Node ptr

41. node new node (ex) Insertion and Deletion node node node deleted

42. 항공 예약 시스템 • 비행 제어 데이터 비행기번호, 시간, 좌석수, 출발지,도착지 • 고객 요청 데이터 종류(질의, 예약, 취소) 이름, 비행기번호, 시간

43. #define numflight 100 typedef struct node { char name[20]; struct node *next; } nodeptr; typedef struct queue { char name[20]; nodeptr *front, *rear: } queueptr;

44. ** 비행기 예약 구조체 typedef struct flighttype { char fltno[4]; int capacity; int count; nodeptr *flthead; queueptr *waitlist; } flight; Flight flight[numflight];

45. 주 프로그램 char command struct flighttype *t; Void airline(void) { int i; nodeptr *p, *pred; t = flight;

46. ** 초기화 For (i=0; i < numflight; i++) scanf(“%4s %d”, t->fltno, &t->seat); t->count = 0; pred = (struct node *) malloc; t->flthd = pred; pred->next = NULL; p = (struct node *) maloc; t->front = p; t->rear = p; p->next = NULL; }

47. While (command != ESC) { scanf(“%c”, &command); switch (command) { case ‘I’ : inquire( ); break; case ‘R’ : reserve( ); break; case ‘C’ : cancel( ); break; }