An explanation of how to calculate the Cartesian product of multiple sets in PHP

Cartesian productrefers to the Cartesian product (Cartesian product) of two sets X and Y in mathematics, also known as direct product, expressed as X*Y, the first object is X is a member of Y and the second object is one of the members of all possible ordered pairs of Y.

Assume that the setA={a,b}and the setB={0,1,2}, then the Cartesian product of the two sets is{(a,0),(a,1),(a,2),(b,0),(b,1),(b,2)}
Idea:First calculate theCartesian productof the first set and the second set, and save the result as a new set.
Then use the new set to calculate the Cartesian product with the next set, and loop in this manner until the Cartesian product is calculated with the last set.
For example, there are the following sets, and the Cartesian product needs to be calculated

The code is as follows:

Output:

Array( [0] => 白色透气37码男款 [1] => 白色透气37码女款 [2] => 白色透气38码男款 [3] => 白色透气38码女款 [4] => 白色透气39码男款 [5] => 白色透气39码女款 [6] => 白色防滑37码男款 [7] => 白色防滑37码女款 [8] => 白色防滑38码男款 [9] => 白色防滑38码女款 [10] => 白色防滑39码男款 [11] => 白色防滑39码女款 [12] => 黑色透气37码男款 [13] => 黑色透气37码女款 [14] => 黑色透气38码男款 [15] => 黑色透气38码女款 [16] => 黑色透气39码男款 [17] => 黑色透气39码女款 [18] => 黑色防滑37码男款 [19] => 黑色防滑37码女款 [20] => 黑色防滑38码男款 [21] => 黑色防滑38码女款 [22] => 黑色防滑39码男款 [23] => 黑色防滑39码女款 [24] => 红色透气37码男款 [25] => 红色透气37码女款 [26] => 红色透气38码男款 [27] => 红色透气38码女款 [28] => 红色透气39码男款 [29] => 红色透气39码女款 [30] => 红色防滑37码男款 [31] => 红色防滑37码女款 [32] => 红色防滑38码男款 [33] => 红色防滑38码女款 [34] => 红色防滑39码男款 [35] => 红色防滑39码女款 )

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