Question

我尝试使用Lomuto's Partitiong方法实现迭代 QuickSort ，因此我尝试实现堆栈保存一对索引，用于定义要分区的子数组，使用struct数组和两个fields：iBeg，iEnd并仅存储/访问{{1}元素。

以下是代码：

end

明显愚蠢的数组赋值function [sorted] = iterativeQuickSort(A) % Accepts 1xN unsorted integer array. % Returns a sorted copy. % See also Partition. % Starting and ending indexes of unsorted array. iBeg = 1; iEnd = numel(A); % Struct holding A's subarrays star/end indexes resulting from partitioning. stack_elem = struct('iBeg', iBeg, 'iEnd', iEnd); stack(end + 1) = stack_elem; % push on stack while numel(stack) != 0 % Extract last pair of indexes. iBeg = stack(end).iBeg; iEnd = stack(end).iEnd; stack(end) = []; % pop from stack % Get pivot index and array after rearranging elements around the pivot. [B, pivotIndex] = Partition(A, iBeg, iEnd); A = B; % Store indexes of the next two subarrays defined by the pivot index, % if their sizes are > 0. if pivotIndex - 1 > iBeg stack_elem = struct('iBeg', iBeg, 'iEnd', pivotIndex - 1); stack(end + 1) = stack_elem; end if pivotIndex + 1 < iEnd stack_elem = struct('iBeg', pivotIndex + 1, 'iEnd', iEnd); stack(end + 1) = stack_elem; end end sorted = A; end function [A, pivotIndex] = Partition (A, iBeg, iEnd) % Accepts 1xN integer array. % Two integers - start and end indexes current subarray of A. % Returns index of pivot element of current subarray partition % and A after swaps. pivotValue = A(iEnd); % Choose last element to be pivot. pivotIndex = iBeg; % Initialize pivot index to start of subarray. for i = iBeg : iEnd % Iterate over current subarray if A(i) <= pivotValue % Push elements <= pivot in front of pivot index. % Place element at i-th position before element with pivot index. [A(i), A(pivotIndex)] = swapElements(A(pivotIndex), A(i)); % Account for the swap, go to next element. pivotIndex = pivotIndex + 1; end end % Bring the element used as pivot to its place [A(iEnd), A(pivotIndex)] = swapElements(A(pivotIndex), A(iEnd)); end function [elem2, elem1] = swapElements(elem1, elem2) [elem2, elem1] = deal(elem1, elem2); end用于表示在执行函数A = B后保留swaps引起的元素更改。

当前状态似乎是一个无限循环，其原因我无法识别，因此任何建议和建议都将不胜感激！

输入：

Partition(A, iBeg, iEnd)

预期产出：

A = [5,   4,   6,   2,   9,   1,   7,   3];
S = iterativeQuickSort(A)

电流输出：永不从功能返回，仅通过强制制动停止：ctrl + c。

注意：分区功能的实现和应用与可能重复的那个不同。

Answer 1

您的Partition函数出错。如果你看一下维基百科页面上的伪代码，你会发现循环条件是：

for j := lo to hi - 1 do

Partition功能中的相应行是：

  for i = iBeg : iEnd        % Iterate over current subarray

转到iEnd代替iEnd - 1，您需要将数据透视值与自身进行比较，最后得到一个偏离一个的数据透视索引。只需将此行更改为：

  for i = iBeg : iEnd-1      % Iterate over current subarray

QuickSort迭代实现中的无限循环？

1 个答案: