quicksort

问题 Following text from quick sort section in algorithms book by Robert Sedwick. By choosing the three elements from the left, middle, and right of the array, we can incorporate sentinels into this scheme. Sort three elements, then exchange one in the middle with a[r-1] , and then run the partitioning algorithm on a[l+1],...,a[r-2] . This improvement is called the median of three method. The median of three method helps quick sort in three ways. It makes the worst case much more unlikely to occur

问题 I really like the qsort function in C. It's so easy to use and allows me to procrastinate learning C++ template types. I have a few questions about this: Is the algorithm used always a quicksort or is it compiler-implementation-dependent? Would you recommend using this function or is there a real benefit to templates? Are there any things I should watch out for to avoid security problems/segfaults? 回答1: Is the algorithm used always a quicksort or is it compiler-implementation-dependent? It is

问题 I am trying to write a simple algorithm for moving the elements around pivot such that the elements on the left of pivot is smaller than the pivot and the element on the right of pivot is greater than it (the same step in quick sort). I have written code that works, but after that I changed the algorithm to the below, and it is not working. The idea of the algorithm is simple. Have two pointers, one at the beginning of the array and one at the end of array. If the elements pointed by i are

问题 Sadly, I've got problems with Quicksort as well. I've discussed it with other students and tried the standard troubleshooting methods. But I can't find what I'm doing wrong... static int partition(int[] A) { int pivot, i, j; i = 0; j = A.Length; pivot = A[i]; do { do { i++; } while (A[i] < pivot || i < j); do { j--; } while (A[j] > pivot); swap(ref A[i], ref A[j]); } while (i < j); if (i <= j) { swap(ref A[i], ref A[j]); swap(ref A[0], ref A[j]); } return j; } static void swap(ref int a, ref

问题 This question already has answers here : is it possible to do quicksort of a list with only one passing? (3 answers) Why is the minimalist, example Haskell quicksort not a “true” quicksort? (11 answers) Closed 5 years ago . Here's an example from Learn you a Haskell: quicksort :: (Ord a) => [a] -> [a] quicksort [] = [] quicksort (x:xs) = let smallerSorted = quicksort [a | a <- xs, a <= x] biggerSorted = quicksort [a | a <- xs, a > x] in smallerSorted ++ [x] ++ biggerSorted It seems that the

问题 It seems I'm missing something very simple: what are advantages of a Binary Heap for a Priority Queue comparing, say, with quick-sorted array of values? In both cases we keep values in an array, insert is O(logN), delete-max is O(1) in both cases. Initial construction out of a given array of elements is O(NlogN) in both cases, though the link http://en.wikipedia.org/wiki/Heap_%28data_structure%29 suggests faster Floyd's algorithm for the Binary Heap construction. But in case of a queue the

问题 I am reading some text which claims this regarding the ordering of the two recursive Quicksort calls: ... it is important to call the smaller subproblem first, this in conjunction with tail recursion ensures that the stack depth is log n. I am not at all sure what that means, why should I call Quicksort on the smaller subarray first? 回答1: Look at quicksort as an implicit binary tree. The pivot is the root, and the left and right subtrees are the partitions you create. Now consider doing a

问题 It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. Closed 7 years ago . I recently read about time complexity and I found out that Quick sort has an average time complexity of O(nlog(n)) . Question 1: What I do not understand is how is the log(n) present in the time complexity

问题 I'm learning Idris and I thought I'd try to implement Quicksort for Vect types. But I'm having a hard time with the utility method that should, given a pivot element and a vector, split the vector in two, one with the elements ≤ pivot and another with those > pivot. This is trivial for lists: splitListOn : Ord e => (pivot : e) -> List e -> (List e, List e) splitListOn pivot [] = ([], []) splitListOn pivot (x :: xs) = let (ys, zs) = splitListOn pivot xs in if x <= pivot then (x :: ys, zs) else

问题 This was a problem of CLR (Introduction to Algorithms) The question goes as follow: Suppose that the splits at every level of quicksort are in the proportion 1 - α to α, where 0 < α ≤ 1/2 is a constant. Show that the minimum depth of a leaf in the recursion tree is approximately - lg n/ lg α and the maximum depth is approximately -lg n/ lg(1 - α). (Don't worry about integer round-off.)http://integrator-crimea.com/ddu0043.html I'm not getting how to reach this solution. as per the link they