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I have a vector of doubles. I want to sort it from highest to lowest, and get the indices of the top K elements. std::sort just sorts in place, and does not return the indices I believe. What would be a quick way to get the top K indices of largest elements?
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In more details it is implemented using hybrid of QuickSort, HeapSort and InsertionSort.By default, it uses QuickSort but if QuickSort is doing unfair partitioning and taking more than N*logN time, it switches to HeapSort and when the array size becomes really small, it switches to InsertionSort.
Sorting an Unordered Set: An Unordered Set can be sorted by copying its elements to a Vector and then using the sort() method of the STL. For a better understanding of its implementation, refer to the well-commented C++ code given below.
Sorting a Vector in C++ in Ascending order A vector in C++ can be easily sorted in ascending order using the sort() function defined in the algorithm header file. The sort() function sorts a given data structure and does not return anything. The sorting takes place between the two passed iterators or positions.
Here, first – is the index (pointer) of the first element in the range to be sorted. last – is the index (pointer) of the last element in the range to be sorted. For example, we want to sort elements of an array 'arr' from 1 to 10 position, we will use sort(arr, arr+10) and it will sort 10 elements in Ascending order.
you could use the nth_element STL algorithm - this will return you the N greatest elements ( this is the fastest way,using stl ) and then use .sort on them,or you could use the partial_sort algorithm,if you want the first K elements to be sorted (:
Using just .sort is awful - it is very slow for the purpose you want.. .sort is great STL algorithm,but for sorting the whole container,not just the first K elements (; it's not an accident the existung of nth_element and partial_sort ;)
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