Methods insert k o inserts the item k o and returns a

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methods: insert (k, o): inserts the item (k, o) and returns a locator for it min (): returns the locator of an item with smallest key remove (l): remove the item with locator l replaceKey (l, k): replaces the key of the item with locator l replaceElement (l, o): replaces with o the element of the item with locator l locators (): returns an iterator over the locators of the items in the priority queue Locator-based dictionary methods: insert (k, o): inserts the item (k, o) and returns its locator find (k): if the dictionary contains an item with key k, returns its locator, else return a special null locator remove (l): removes the item with locator l and returns its element locators (), replaceKey (l, k), replaceElement (l, o)
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4/1/2013 10:43 AM Locators 5 Possible Implementation The locator is an object storing key element position (or rank) of the item in the underlying structure In turn, the position (or array cell) stores the locator Example: binary search tree with locators 3 a 6 d 9 b 1 g 4 e 8 c
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4/1/2013 10:43 AM Locators 6 Positions vs. Locators Position represents a “place” in a data structure related to other positions in the data structure (e.g., previous/next or parent/child) often implemented as a pointer to a node or the index of an array cell Position-based ADTs (e.g., sequence and tree) are fundamental data storage schemes Locator identifies and tracks a (key, element) item unrelated to other locators in the data structure often implemented as an object storing the item and its position in the underlying structure Key-based ADTs (e.g., priority queue and dictionary) can be augmented with locator-based methods
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