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Extensible Array C and Data Structures Baojian Hua

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1 Extensible Array C and Data Structures Baojian Hua

2 Linear Data Structures A linear list (list) consists of: a collection of data elements e1, e2, …, en elements are ordered: e1 ≤ e2 ≤ … ≤ en ei is called an predecessor of e_{i+1} e_{i+1} is called a successor of ei every element has at most one successor and one predecessor

3 Linear Data Structures Typical operations on linear list : // create an empty list newList (); // the length of a list l length (list l); // insert element x at position i in l, 0<=i

4 Polymorphic Abstract Data Types in C // in “list.h” #ifndef LIST_H #define LIST_H typedef struct listStruct *list; list newList (); int length (list l); poly nth (list l, int n); // “poly”? void insert (list l, poly x, int i); poly delete (list l, int i); void foreach (list l, void (*f)(poly)); #endif

5 Implementations Two typical implementation techniques: array-based linked structure-based We next consider the first, and leave the second to the next slide

6 Implementation Using Array The straightforward method to implement this interface (ADT) is to use an array and the array may not be full, so we must keep a “ tail ” tag to record its tail (the position of its last elements) 0 n-1

7 Implementation Using Array The straightforward method to implement this interface is to use an array and the array may not be full, so we must keep a “ tail ” tag to record its tail (the position of its last elements) 0 n-1 tail

8 Array-based Implementation // Combine these above observations, we have: // in file “arrayList.c” #include #include “list.h” #define INIT_LENGTH 32 #define EXT_FACTOR 2 struct listStruct { poly *array; int max; int tail; }; 0 n-1 array max tail l

9 Operation: “ newList ” list newList () { list l = (list)malloc (sizeof (*l)); l->array = malloc (INIT_LENTH * sizeof(poly)); l->max = INIT_LENTH; l->tail = 0; return l; }

10 Operation: “ newList ” list newList () { list l = (list)malloc (sizeof (*l)); l->array = malloc (INIT_LENTH * sizeof(poly)); l->max = INIT_LENTH; l->tail = 0; return l; } $#%& l

11 Operation: “ newList ” list newList () { list l = (list)malloc (sizeof (*l)); l->array = malloc (INIT_LENTH * sizeof(poly)); l->max = INIT_LENTH; l->tail = 0; return l; } 0 n-1 array l

12 Operation: “ newList ” list newList () { list l = (list)malloc (sizeof (*l)); l->array = malloc (INIT_LENTH * sizeof(poly)); l->max = INIT_LENTH ; l->tail = 0; return l; } 0 n-1 array l

13 Operation: “ newList ” list newList () { list l = (list)malloc (sizeof (*l)); l->array = malloc (INIT_LENTH * sizeof(poly)); l->max = INIT_LENTH ; l->tail = 0; return l; } 0 n-1 array max tail l

14 Operation: “ length ” int length (list l) { // note that we omit such checks in the next // for clarity. However, You should always do // such kind of checks in your code. assert(l); return l->tail; } 0 n-1 array max tail l

15 Operation: “ nth ” poly nth (list l, int i) { if (i =l->tail) error (“invalid index”); poly temp; temp = *((l->array)+i); return temp; } 0 n-1 array max tail l

16 Operation: “ nth ” poly nth (list l, int i) { if (i =l->tail) error (“invalid index”); poly temp; temp = *((l->array)+i); return temp; } 0 n-1 array max tail l i temp

17 Operation: “ insert ” void insert (list l, poly x, int i) { if (i l->tail) error (“invalid index”); //move the data …; } 0 n-1 array max tail l i

18 Operation: “ insert ” void insert (list l, poly x, int i) { if (i l->tail) error (“invalid index”); for (int j=l->tail; j>i; j--) (l->array)[j] = (l->array)[j-1]; …; } 0 n-1 array max tail l i j

19 Operation: “ insert ” void insert (list l, poly x, int i) { if (i l->tail) error (“invalid index”); for (int j=l->tail; j>i; j--) (l->array)[j] = (l->array)[j-1]; …; } 0 n-1 array max tail l i j

20 Operation: “ insert ” void insert (list l, poly x, int i) { if (i l->tail) error (“invalid index”); for (int j=l->tail; j>i; j--) (l->array)[j] = (l->array)[j-1]; …; } 0 n-1 array max tail l i j

21 Operation: “ insert ” void insert (list l, void *x, int i) { if (i l->tail) error (“invalid index”); for (int j=l->tail; j>i; j--) (l->array)[j] = (l->array)[j-1]; (l->array)[i] = x; } x 0 n-1 array max tail l i j

22 Operation: “ insert ” void insert (list l, void *x, int i) { if (i l->tail) error (“invalid index”); for (int j=l->tail; j>i; j--) (l->array)[j] = (l->array)[j-1]; (l->array)[i] = x; (l->tail)++; } x 0 n-1 array max tail l i j

23 Perfect? What if the initial input arguments look like this one? direct data movement will incur an out-of-bound error! 0 n-1 array max tail l i

24 Extensible Array void insert (list l, poly x, int i) { if (i l->tail) error (“invalid index”); // if l is full, extend l->array by a factor… if (l->tail==l->max) { l->array = realloc (l->array, EXT_FACTOR*(l->max)*sizeof(poly)); l->max *= EXT_FACTOR; } // data movement as discussed above…; }

25 Extensible Array 0 n-1 array max tail l i 02n-1 i l->array = realloc (l->array, EXT_FACTOR*(l->max)*sizeof(poly)); n-1

26 Extensible Array 0 n-1 array max tail l i 02n-1 i n-1 l->array = realloc (l->array, EXT_FACTOR*(l->max)*sizeof(poly));

27 Extensible Array 0 n-1 array max tail l i 02n-1 i l->max *= EXT_FACTOR; l->array = realloc (l->array, EXT_FACTOR*(l->max)*sizeof(poly));

28 Extensible Array array max tail l 02n-1 i n-1

29 Operation: “ delete ” The “ delete ” operation is reverse operation of the “ insert ” operation also involves data movement should we shrink the extensible array, when there are few elements in it (say ½ data item left)? See the programming assignment

30 Operation: “ foreach ” void foreach (list l, void (*f)(poly)) { for (int i=0; i tail; i++) f (*(l->array + i)); return; } 0 n-1 array max tail l

31 Summary Linear list ADT: a collection of ordered data element each item has no more than one successor or predecessor Extensible array-based implementation maintain internally a dynamically extensible array bad performance with insert or delete space waste


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