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Marcos Cerioni
Asked: 2020-07-18 06:08:48 +0800 CST 2020-07-18 06:08:48 +0800 CST

Copy indices from one array to another array in C

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I need to copy the indices from one array to another in C, as efficiently as possible.

For example if I have the array: 

datos = [4,8,10,12,15]

Array 2 should give me the following:

indices = [0,1,2,3,4]

In other words, somehow (in the example) the value "4" should be associated with the index "0", the value "8" with the index "1" and so on...

The data will always be ordered from smallest to largest.

The goal would be to make it as efficient as possible, I don't want to use a for, which will give me order n (O(n)).

What I tried to do is a memcpy, but all I managed to do was copy the same array (only the data).

Thank you!!

array

1 Answers

  1. Best Answer

    Example of a for to do what you ask but parallelized with OpenMP.

    int count = datos.length; //aquí iría el tamaño de tu array datos
int indices[100];
#pragma omp parallel for
for(int i=0; i<count; i++) //i es privada por defecto al crearse dentro del for
{
    indices[i]=i;
}

    For it to work you must include the omp.h library and compile with the -fopenmp flag

    Compilation example:

    g++ test.cpp -o test -fopenmp
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