JavaScript array Sort out! Indices problem

Given an array A of non-negative integers of size m. Your task is to sort the array in non-decreasing order and print out the original indices of the new sorted array. e.g.A={4,5,3,7,1}

After sorting the new array becomes A={1,3,4,5,7}.

The required output should be “4 2 0 1 3”

Answer

You need to pair (tuple) the value with the original index. After mapping the tuples, sort by the value and finally map the original (now sorted) indices.

const sortValuesAndGetOriginalIndices = (arr) => arr
  .map((element, index) => [element, index])
  .sort(([v1], [v2]) => v1 - v2)
  .map(([value, index]) => index);

const arr = [4, 5, 3, 7, 1];
const indices = sortValuesAndGetOriginalIndices(arr);

console.log(...indices); // [4, 2, 0, 1, 3]

If you want to return the sorted values and the indicies, you can reduce at the end:

const enhancedSort = (arr) => arr
  .map((element, index) => [element, index])
  .sort(([v1], [v2]) => v1 - v2)
  .reduce(({ values, indices }, [v, i]) =>
    ({
      values: [...values, v],
      indices: [...indices, i]
    }),
    { values: [], indices: [] });

const arr = [4, 5, 3, 7, 1];
const { values, indices } = enhancedSort(arr);

console.log(...values);  // [1, 3, 4, 5, 7]
console.log(...indices); // [4, 2, 0, 1, 3]

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