Route Tracer

In this challenge, the work area will be a 4x4 matrix containing three types of characters:

• @ Your position.
• - A blank spot.
• &, #, $ Collectible items.

From your starting point in the grid, you have to trace a route placing a x in every spot visited, following a sequence of letters with the directions to take:

• l Left
• r Right
• u Up
• d Down

input = "luur"
// left, up, up, right

grid = [
["-", "-", "-", "#"]
["-", "-", "$", "-"]
["-", "-", "-", "@"]
["-", "&", "-", "-"] ]

result = { route = [
["-", "-", "x", "x"],
["-", "-", "x", "-"],
["-", "-", "x", "@"],
["-", "&", "-", "-"] ],
items: "$#" }

When moves are finished, you will have a new grid with the traced given route (a route made of x chars), and a series of items collected along the way.

Given a matrix grid and a string with the directions to take input, implement a function that returns an object literal containing the traced route as a new matrix and the items collected as a string.

Examples

function routeTracer([
  ["-", "#", "-", "-"],
  ["$", "#", "@", "&"],
  ["-", "#", "$", "&"],
  ["$", "-", "&", "-"]
], "lddr",) ➞ {
  route: [
 ["-", "#", "-", "-"],
  ["$", "x", "@", "&"],
  ["-", "x", "$", "&"],
  ["$", "x", "x", "-"]
  ],
  items: "##&"
}

Notes

• The starting position must not be changed in the new matrix.
• The x will overwite the symbol already present in the spot visited.
• In the returned string, items have to appear in the order you collected them. Watch out for the blank spots: they're not collectible!
• Don't worry about "out of bounds" cases, instruction strings contain only valid routes.
• Instruction strings will have different lengths.