Question

How to rearrange an array and set arr[i] to arr[arr[index]] to index in C++

Answer 1

#include <iostream>

void rearrange_array(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        arr[i] += (arr[arr[i]] % size) * size;
    }
 
    for (int i = 0; i < size; i++) {
        arr[i] /= size;
    }
}

int main()
{
    int arr[] = {3, 5, 0, 2, 1, 4};
    int size = sizeof(arr)/sizeof(arr[0]);
    
    // arr[arr[0]] = 2 -> arr[0] = 2
    // arr[arr[1]] = 4 -> arr[1] = 4
    // arr[arr[2]] = 3 -> arr[2] = 3
    // arr[arr[3]] = 0 -> arr[3] = 0
    // arr[arr[4]] = 5 -> arr[4] = 5
    // arr[arr[5]] = 1 -> arr[5] = 1

     rearrange_array(arr, size);
 
    for (int i = 0; i < size; i++) {
        std::cout << arr[i] << " ";
    }
}




/*
run:

2 4 3 0 5 1 

*/

 

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