Use of Position in Adaptable Priority Queue





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What is the use of Position in Adaptable priority queue(List based heap for keys) when we have to anyway pass the Entry reference to the functions remove(k), replaceKey(k).
i.e. If I have some reference "ref" to an entry in queue then I can simply call remove(ref) and replaceKey(ref) and that would still take O(1) time. Why would I need special position for this?










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    What is the use of Position in Adaptable priority queue(List based heap for keys) when we have to anyway pass the Entry reference to the functions remove(k), replaceKey(k).
    i.e. If I have some reference "ref" to an entry in queue then I can simply call remove(ref) and replaceKey(ref) and that would still take O(1) time. Why would I need special position for this?










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      What is the use of Position in Adaptable priority queue(List based heap for keys) when we have to anyway pass the Entry reference to the functions remove(k), replaceKey(k).
      i.e. If I have some reference "ref" to an entry in queue then I can simply call remove(ref) and replaceKey(ref) and that would still take O(1) time. Why would I need special position for this?










      share|improve this question














      What is the use of Position in Adaptable priority queue(List based heap for keys) when we have to anyway pass the Entry reference to the functions remove(k), replaceKey(k).
      i.e. If I have some reference "ref" to an entry in queue then I can simply call remove(ref) and replaceKey(ref) and that would still take O(1) time. Why would I need special position for this?







      java data-structures






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      asked Nov 16 '18 at 19:47









      rohit bhadoriarohit bhadoria

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          1. It doesn't make any sense at all to implement a heap as a linked list. Heaps are inherently neally complete binary trees. You can store a heap in an array because it's easy to compute the array index of a node's children: the children of the node at position i live at positions 2i + 1 and 2i+2. It's massively more efficient to find the ith element of an array than the ith element of a linked list.


          2. For adaptable priority queues, The array(heaps) is a sequence of references to position instances, each of which stores a key, value, and the current index of the item within the array. The user will be given a reference to the Position instance for each inserted element.When we perform priority queue operations on our heap, and items are relocated
            within our structure, we reposition the position instances within the array and we
            update the third field of each position to reflect its new index within the array, and the update will take O(log(n)) time complexity.







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            1. It doesn't make any sense at all to implement a heap as a linked list. Heaps are inherently neally complete binary trees. You can store a heap in an array because it's easy to compute the array index of a node's children: the children of the node at position i live at positions 2i + 1 and 2i+2. It's massively more efficient to find the ith element of an array than the ith element of a linked list.


            2. For adaptable priority queues, The array(heaps) is a sequence of references to position instances, each of which stores a key, value, and the current index of the item within the array. The user will be given a reference to the Position instance for each inserted element.When we perform priority queue operations on our heap, and items are relocated
              within our structure, we reposition the position instances within the array and we
              update the third field of each position to reflect its new index within the array, and the update will take O(log(n)) time complexity.







            share|improve this answer




























              1















              1. It doesn't make any sense at all to implement a heap as a linked list. Heaps are inherently neally complete binary trees. You can store a heap in an array because it's easy to compute the array index of a node's children: the children of the node at position i live at positions 2i + 1 and 2i+2. It's massively more efficient to find the ith element of an array than the ith element of a linked list.


              2. For adaptable priority queues, The array(heaps) is a sequence of references to position instances, each of which stores a key, value, and the current index of the item within the array. The user will be given a reference to the Position instance for each inserted element.When we perform priority queue operations on our heap, and items are relocated
                within our structure, we reposition the position instances within the array and we
                update the third field of each position to reflect its new index within the array, and the update will take O(log(n)) time complexity.







              share|improve this answer


























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                1








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                1. It doesn't make any sense at all to implement a heap as a linked list. Heaps are inherently neally complete binary trees. You can store a heap in an array because it's easy to compute the array index of a node's children: the children of the node at position i live at positions 2i + 1 and 2i+2. It's massively more efficient to find the ith element of an array than the ith element of a linked list.


                2. For adaptable priority queues, The array(heaps) is a sequence of references to position instances, each of which stores a key, value, and the current index of the item within the array. The user will be given a reference to the Position instance for each inserted element.When we perform priority queue operations on our heap, and items are relocated
                  within our structure, we reposition the position instances within the array and we
                  update the third field of each position to reflect its new index within the array, and the update will take O(log(n)) time complexity.







                share|improve this answer














                1. It doesn't make any sense at all to implement a heap as a linked list. Heaps are inherently neally complete binary trees. You can store a heap in an array because it's easy to compute the array index of a node's children: the children of the node at position i live at positions 2i + 1 and 2i+2. It's massively more efficient to find the ith element of an array than the ith element of a linked list.


                2. For adaptable priority queues, The array(heaps) is a sequence of references to position instances, each of which stores a key, value, and the current index of the item within the array. The user will be given a reference to the Position instance for each inserted element.When we perform priority queue operations on our heap, and items are relocated
                  within our structure, we reposition the position instances within the array and we
                  update the third field of each position to reflect its new index within the array, and the update will take O(log(n)) time complexity.








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                answered Jan 9 at 13:47









                minglyuminglyu

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