Shuffle an array according to the given order of elements

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 the 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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