Custom Sort Array

Puzzle

Write a function rearrange_array which takes a contents array and an indexes array and mutates contents so that each element ends up in their new index.

Examples

// INPUT
> var contents = ["dog", "cat", "rat"];
> var indexes = [2, 0, 1];
> rearrange_array(contents, indexes);

// OUTPUT
["cat", "rat", "dog"];

Solution

How It Works

1. (Optional) Validate input parameters.
   • Ensure contents and indexes are the same length.
   • Ensure indexes elements are unique, sequential values from 0..indexes.length.
2. Create an empty output array to return.
3. Loop through the contents array elements.
   • Add the current element in the loop to the output array, based on the corresponding index value in indexes.
4. Return output.

Code

/**
*
* Custom sorts an input array based on values in an indexes array.
*
* @param {array} contents - Input array
* @param {array} indexes - Array with position information for the new order of the input elements
* @return {array} output - Custom sorted array
*
**/
function rearrange_array(contents, indexes) {

  // 1. (OPTIONAL) VALIDATION

  // Ensure contents and indexes are arrays
  if (!Array.isArray(contents) || !Array.isArray(indexes)) {
    throw new TypeError("contents and indexes parameters must be arrays");
  }

  // Ensure both arrays have the same length
  if (contents.length !== indexes.length) {
    throw new RangeError("contents and indexes parameters must be the same length");
  } else {

    // Ensure indexes values are within range and unique
    var indexes_seen = [];

    // Index elements must be within 0..indexes.length
    for (var i = 0; i < indexes.length; i++) {

      if(typeof indexes[i] !== "number") {

        throw new TypeError("indexes contains non-numeric elements");

      };

      if ((indexes[i] < 0) || (indexes[i] > contents.length - 1)) {

        throw new RangeError("indexes contains an element that is out of range");

      };

      // Index elements must be unique
      if (indexes_seen.indexOf(indexes[i]) !== -1) {
        throw new RangeError("indexes contains non-unique elements");
      };

      indexes_seen.push(indexes[i]);

    };

    // 2. OUTPUT ARRAY
    var output = [];


    // 3. MAIN LOOP
    for (var i = 0; i < indexes.length; i++) {
      output[indexes[i]] = contents[i];
    };

    return output;

  };
  
};

Variations

1-based Indexes Array

A popular variation of the puzzle involves the indexes array being a 1-base array from 1..contents.length - 1 rather than 0..contents.length.

Alphabetical Indexes Array

A tricker variation involves the indexes array being an alphabetical array rather than a numerical array (e.g. ["c", "a", "b"] rather than [2, 0, 1]). To solve this, incorporate a step that converts an alphabetical array to a numerical range.