How to rearrange an array by indices array?

Question

Given an array arr and an array of indices ind, I\'d like to rearrange arr in-place to satisfy the given indices. For exa

Answer 1

Below, one may find a PARTIAL solution for a case when we have only ONE cycle, i.e.

var arr = ["A", "B", "C", "D", "E", "F"];
var ind = [4, 2, 5, 0, 1, 3];

function rearrange( i, arr, ind, temp ){
    if( temp ){
        if( arr[ind[i]] ){
            var temp2 = arr[ind[i]];
            arr[ind[i]] = temp;
            rearrange( ind[i], arr, ind, temp2 );
        }
        else{                                           // cycle
            arr[ind[i]] = temp;
            // var unvisited_index = ...;
            // if( unvisited_index ) rearrange( unvisited_index, arr, ind, "" );
        }
    }
    else{
        if( i == ind[i] ){
            if( i < arr.length ) rearrange( i + 1, arr, ind, temp );    
        }
        else{
            temp = arr[ind[i]];
            arr[ind[i]]=arr[i];
            arr[i] = "";
            i = ind[i];
            rearrange(i, arr, ind, temp );
        }
    }
}

rearrange( 0, arr, ind, "" );

To make this solution to work for a general case, we need to find total numbers of unique cycles and one index from each of them.

For the OP example:

var arr = ["A", "B", "C", "D", "E", "F"];
var ind = [4, 0, 5, 2, 1, 3];

There are 2 unique cycles:

4 -> 1 -> 0 -> 4
5 -> 3 -> 2 -> 5

If one runs

rearrange( 0, arr, ind, "" );
rearrange( 5, arr, ind, "" );

S(he) will get desirable output for the OP problem.