Shuffle an array according to the given order of elements

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Shuffle an array according to the given order of elements

Vinay Khatri
Last updated on June 9, 2022

    Problem

    Given two integer arrays of the same size, arr [] and index[] , reorder elements in arr [] according to the given index array.

    Sample Input

    [10, 11, 12]
    [1, 0, 2]

    Sample Output

    11, 10, 12
    0, 1, 2

    Approach

    We can traverse through 0 to n-1 (where n is the size of the arrays) and keep placing the current elements at correct indices. This will ultimately give us the required array. For this, we can swap index[i] with index[index[i]] and arr[index[i]] with arr[i] .

    C++ Programming

    #include<bits/stdc++.h>
    using namespace std;
    void solve(int a[], int n, int index[]){
        for(int i=0;i<n;i++){
            int temp = index[i];
            swap(index[index[i]], index[i]);
            swap(a[temp], a[i]);
        }
    }
    int main(){
        int a[] = {50, 40, 70, 60, 90};
        int index[] = {3,  0,  4,  1,  2};
        int n =sizeof(a)/sizeof(a[0]);
        solve(a, n, index);
        for(int i=0;i<n;i++) cout<<a[i]<<" ";
        cout<<"\n";
        for(int i=0;i<n;i++) cout<<index[i]<<" ";
    }

    Output

    40 60 90 50 70 
    0 1 2 3 4

    C Programming

    #include<stdio.h>
    void swap(int *x, int *y)
    {
        int temp = *x;
        *x = *y;
        *y = temp;
    }
    
    void solve(int a[], int n, int index[]){
        for(int i=0;i<n;i++){
            int temp = index[i];
            swap(&index[index[i]], &index[i]);
            swap(&a[temp], &a[i]);
        }
    }
    int main(){
        int a[] = {50, 40, 70, 60, 90};
        int index[] = {3,  0,  4,  1,  2};
        int n =sizeof(a)/sizeof(a[0]);
        solve(a, n, index);
        for(int i=0;i<n;i++) printf("%d ", a[i]);
        printf("\n");
        for(int i=0;i<n;i++) printf("%d ", index[i]);
    }

    Output

    40 60 90 50 70 
    0 1 2 3 4

    Python Programming

    def solve(a, index, n):
        for i in range(0, n):
            temp = index[i]
            t = index[index[i]]
            index[index[i]] = index[i]
            index[i] = t
            t = a[temp]
            a[temp] = a[i]
            a[i] = t
    
    
    a = [50, 40, 70, 60, 90]
    index = [3,  0,  4,  1,  2]
    n = len(a)
    solve(a, index, n)
    print(a)
    print(index)

    Output

    [40, 60, 90, 50, 70] 
    [0, 1, 2, 3, 4]
    

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    Tags:
    array

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