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Revise the array list implementation given in Section 7.2.1 so that when the ac- tual number of elements, n, in the array goes below N/4, where N is the array capacity, the array shrinks to half its size.

Revise the array list implementation given in Section 7.2.1 so that when the ac- tual number of elements, n, in the array goes below N/4, where N is the array capacity, the array shrinks to half its size.

C++ Programming: From Problem Analysis to Program Design
C++ Programming: From Problem Analysis to Program Design
8th Edition
ISBN:9781337102087
Author:D. S. Malik
Publisher:D. S. Malik
Chapter17: Linked Lists
Section: Chapter Questions
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please jelp with C 7.29

C 7.29: Revise the array list implementation given in Section 7.2.1 so that when the ac- tual number of elements, n, in the array goes below N/4, where N is the array capacity, the array shrinks to half its size.

7.2.1 Dynamic Arrays The ArrayList implementation in Code Fragments 7.2 and 7.3 (as well as those for a stack, queue, and deque from Chapter 6) has a serious limitation; it requires that a fixed maximum capacity be declared, throwing an exception if attempting to add an element once full. This a major weakness, because if a user is unsure of the maximum size that will be reached for a collection, there is risk that either too large of an array will be requested, causing an inefficient waste of memory, or that too small of an array will be requested, causing a fatal error when exhausting that capacity. Java's ArrayList class provides a more robust abstraction, allowing a user to add elements to the list, with no apparent limit on the overall capacity. To provide this abstraction, Java relies on an algorithmic sleight of hand that is known as a dynamic array. In reality, elements of an ArrayList are stored in a traditional array, and the precise size of that traditional array must be internally declared in order for the system to properly allocate a consecutive piece of memory for its storage. For example, Figure 7.2 displays an array with 12 cells that might be stored in memory locations 2146 through 2157 on a computer system. 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 Xxxs Figure 7.2: An array of 12 cells, allocated in memory locations 2146 through 2157. Because the system may allocate neighboring memory locations to store other data, the capacity of an array cannot be increased by expanding into subsequent cells. The first key to providing the semantics of an unbounded array is that an array list instance maintains an internal array that often has greater capacity than the current length of the list. For example, while a user may have created a list with five elements, the system may have reserved an underlying array capable of storing eight object references (rather than only five). This extra capacity makes it easy to add a new element to the end of the list by using the next available cell of the array. If a user continues to add elements to a list, all reserved capacity in the underly- ing array will eventually be exhausted. In that case, the class requests a new, larger array from the system, and copies all references from the smaller array into the beginning of the new array. At that point in time, the old array is no longer needed, so it can be reclaimed by the system. Intuitively, this strategy is much like that of the hermit crab, which moves into a larger shell when it outgrows its previous one.
Transcribed Image Text:7.2.1 Dynamic Arrays The ArrayList implementation in Code Fragments 7.2 and 7.3 (as well as those for a stack, queue, and deque from Chapter 6) has a serious limitation; it requires that a fixed maximum capacity be declared, throwing an exception if attempting to add an element once full. This a major weakness, because if a user is unsure of the maximum size that will be reached for a collection, there is risk that either too large of an array will be requested, causing an inefficient waste of memory, or that too small of an array will be requested, causing a fatal error when exhausting that capacity. Java's ArrayList class provides a more robust abstraction, allowing a user to add elements to the list, with no apparent limit on the overall capacity. To provide this abstraction, Java relies on an algorithmic sleight of hand that is known as a dynamic array. In reality, elements of an ArrayList are stored in a traditional array, and the precise size of that traditional array must be internally declared in order for the system to properly allocate a consecutive piece of memory for its storage. For example, Figure 7.2 displays an array with 12 cells that might be stored in memory locations 2146 through 2157 on a computer system. 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 Xxxs Figure 7.2: An array of 12 cells, allocated in memory locations 2146 through 2157. Because the system may allocate neighboring memory locations to store other data, the capacity of an array cannot be increased by expanding into subsequent cells. The first key to providing the semantics of an unbounded array is that an array list instance maintains an internal array that often has greater capacity than the current length of the list. For example, while a user may have created a list with five elements, the system may have reserved an underlying array capable of storing eight object references (rather than only five). This extra capacity makes it easy to add a new element to the end of the list by using the next available cell of the array. If a user continues to add elements to a list, all reserved capacity in the underly- ing array will eventually be exhausted. In that case, the class requests a new, larger array from the system, and copies all references from the smaller array into the beginning of the new array. At that point in time, the old array is no longer needed, so it can be reclaimed by the system. Intuitively, this strategy is much like that of the hermit crab, which moves into a larger shell when it outgrows its previous one.
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