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Today’s topics
• Finish Editor Buffer case study
• Start Map implementation, trees
Reading
• Ch 9
• Ch 13
Café today after class
Lecture
Buffer: Vector vs Stack
!!!!! Vector Stack Buffer() O(1) O(1) ~Buffer() O(1) O(1) moveCursorForward() O(1) O(1) moveCursorBackward() O(1) O(1) moveCursorToStart() O(1) O(N) moveCursorToEnd() O(1) O(N) insertCharacter() O(N) O(1) deleteCharacter() O(N) O(1) Space used 1N 2N
Buffer as linked list
Inspiration: contiguous memory is constraining
• Connect chars without locality
• Linked list to the rescue!
Buffer contains: AB|CDE
// for Buffer class private: struct cellT { char ch; cellT *next; }; cellT *head, *cursor; head cursor
E
A
A B^
C
C D
Cursor design
Where does cursor point?
• To cell^ before^ or^ after?
• Where is cursor if between B & C?
• After E?
• Before A?
• 5 letters, 6 cursor positions…
head
cursor
E A A B^ C C D
Use of dummy cell for linked list Add "dummy cell" to front of list
- Simplifies logic
- Every cell holding actual data has a predecessor
- Cursor can point to cell before insertion point
head
cursor
E A A B^ C C D ? dummy cell Linked list insert/delete void Buffer::insertCharacter(char ch) { cellT *cp = new cellT; cp->ch = ch; cp->next = cursor->next; cursor->next = cp; cursor = cp; } void Buffer::deleteCharacter() { if (cursor->next != NULL) { cellT *old = cursor->next; cursor->next = old->next; delete old; } } Linked list cursor movement void Buffer::moveCursorToBegin() { cursor = head; } void Buffer::moveCursorForward() { if (cursor->next != NULL) cursor = cursor->next; } void Buffer::moveCursorToEnd() { while (cursor->next != NULL) moveCursorForward(); } void Buffer::moveCursorBackward() { if (cursor != head) { cellT *cp = head; while (cp->next != cursor) cp = cp->next; cursor = cp; } Compare implementations !!!!! Vector Stack List Buffer() O(1) O(1) O(1) ~Buffer() O(1) O(1) O(N) moveCursorForward() O(1) O(1) O(1) moveCursorBackward() O(1) O(1) O(N) moveCursorToStart() O(1) O(N) O(1) moveCursorToEnd() O(1) O(N) O(N) insertCharacter() O(N) O(1) O(1) deleteCharacter() O(N) O(1) O(1) Space used 1N 2N 5N
Simple Map implementation Layer on Vector
- Provides convenience with low overhead Define pair struct
- Holds key and value together
- Store Vector Vector sorted or unsorted?
- If sorted, sorted by what? How to implement getValue? How to implement add? Map as Vector !!!!! Unsorted Sorted Map() O(1) O(1) ~Map() O(1) O(1) add() O(N) O(N) getValue() O(N) O(logN) Overhead per entry none none A different strategy Sorting the Vector
- Provides fast lookup, but still slow to insert (because of shuffling) Does a linked list help? - Easy to insert, once at a position - But hard to find position to insert... - Will rearranging pointers help? Bashful Doc Dopey Grumpy Happy Sleepy Sneezy Bashful Doc Dopey Grumpy Happy Sleepy Sneezy Bashful Doc Dopey Grumpy Happy Sleepy Sneezy
