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    <p>I would store these values in two parallel structures. First, have an array of the double values, each of which stores a pointer. Next, store all the strings in a hash table along with an auxiliary integer. The idea is that the pointers in the array point to the nodes in the hash table or trie holding the string associated with the double, while the integer value with each string stores the index of the double paired with that string.</p> <p>To insert a string/double pair into this structure, you add the string to the hash table, append the double to the array, then store a pointer to the new string in the array and the index of the double in the hash table. This has complexity O(k), where k is the length of the string.</p> <p>To change a priority, look up the string in the hash table, then get the index of the double in the array. You can then modify that element to change tye associated priority. This also has complexity O(k).</p> <p>To discard all but the top B key/value pairs, run a selection algorithm on the array to put the top B elements in one part of the array and the remaining C elements in the other. Whenever you perform a swap, follow the pointers out of the array and into the hash table and update the indices of the elements you just swapped. Finally, iterate across the last C elements of the array, follow their pointers back into the hash table, and remove the elements they point at from the table. This takes expected O(n) time to do the selection step, or worst-case O(n) time using the median-of-medians algorithm, followed by O(n) time to remove the elements from the hash table, for an expected runtime of O(n), where n is the number of elements in the structure.</p> <p>To summarize, this gives you O(k) insertion and lookup of any string, where k is the string length, and O(n) retaining of the best elements, where n is the total number of elements. </p>
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    1. UStemplatetypedef
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    1. COThanks for a great response! Do you think std::nth_element will perform as good as implementing my own median-of-medians algorithm or quick-select??
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    2. CO@Akhil- To the best of my knowledge `nth_element` should be fine for this purpose. It's probably implemented using either quickselect or introselect (a quickselect variant that falls back on median-of-medians when it looks like it's degenerating). I'd advise not to implement your own unless it looks like `nth_element` isn't fast enough.
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    3. COThanks @templatetypedef
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