Matlab 最大递归限制为 500 达到错误

Question

嘿，我是 Matlab 的新手，我为快速排序编写了一个简单的代码，但对于某些数组，通常是较长的数组，我的递归失败并给出以下错误： “达到最大递归限制 500。使用 set(0,'RecursionLimit',N) 更改 限制。请注意，超出可用堆栈空间可能会使 MATLAB 和/或 你的电脑。

quic 中的错误”

我认为我的基本情况可能是错误的，但我无法弄清楚我做错了什么。一些帮助将不胜感激。

function A = quicksort(A,left,right)


[A, pivot] = PartitionPivot(A, left, right); %chosen pivot
A = quicksort(A, left, pivot-1); %scan from the left of the array until an element greater than pivot is found and swap it with the element less than the pivot on the right of the pivot
A = quicksort(A, pivot+1, right); %scan from the right of the array until an element less than   pivot is found and swap it with the element greater than the pivot on the left of the pivot
end

function [sortedSub_array,Pivot] = PartitionPivot(Sub_array,left_index,right_index)

% Initialization
S = Sub_array;
left = left_index;
right = right_index;

P = S(left); %pivot
i = left+1;

% Partition
for j = i:right 
    if S(j) < P 
        temp1 = S(j);
        S(j) = S(i);
        S(i) = temp1;
        i = i+1; %increment i only when swap occurs
    end
end
swap1 = S(left);
S(left) = S(i-1);
S(i-1) = swap1;

sortedSub_array = S;
Pivot = P;

Answer 1

我注意到的第一件事是您没有包含停止标准，这意味着算法永远不会停止并且确实会超过任何有限限制。其次，您返回一个枢轴 VALUE，同时将该值用作下一次迭代的枢轴 INDEX。

包含停止标准并返回索引 i 而不是值 P 可以解决您的问题：

function A = quicksort(A,left,right)


if left < right
    [A, pivot] = PartitionPivot(A, left, right); %chosen pivot
    A = quicksort(A, left, pivot-1); %scan from the left of the array until an element greater than pivot is found and swap it with the element less than the pivot on the right of the pivot
    A = quicksort(A, pivot+1, right); %scan from the right of the array until an element less than   pivot is found and swap it with the element greater than the pivot on the left of the pivot
end

end

function [sortedSub_array,PivotIndex] = PartitionPivot(Sub_array,left_index,right_index)

% Initialization
S = Sub_array;
left = left_index;
right = right_index;

P = S(left); %pivot
i = left+1;

% Partition
for j = i:right
    if S(j) < P 
        temp1 = S(j);
        S(j) = S(i);
        S(i) = temp1;
        i = i+1; %increment i only when swap occurs
    end
end
swap1 = S(left);
S(left) = S(i-1);
S(i-1) = swap1;

sortedSub_array = S;
PivotIndex = i-1;

end

顺便说一句，您可以通过使用更少的变量来显着缩短代码。包括对参数数量的检查允许您仅使用数组本身作为参数来调用快速排序。

function A = quicksort(A,left,right)

if nargin == 1
    left = 1;
    right = numel(A);
end

if left < right
    [A, pivot] = PartitionPivot(A, left, right); %chosen pivot
    A = quicksort(A, left, pivot-1); %scan from the left of the array until an element greater than pivot is found and swap it with the element less than the pivot on the right of the pivot
    A = quicksort(A, pivot+1, right); %scan from the right of the array until an element less than   pivot is found and swap it with the element greater than the pivot on the left of the pivot
end

end

function [A, i] = PartitionPivot(A,left,right)

P = A(left); % pivot

A([right left]) = A([left right]);
i = left;

% Partition
for j = left:right-1
    if A(j) < P 
        A([j i]) = A([i j]);
        i = i+1; % increment i only when swap occurs
    end
end
A([right i]) = A([i right]);

end