Source: Codewars

The Challenge: Write a function dirReduc which will take an array of strings and returns an array of strings with the needless directions removed (W<->E or S<->N side by side).

In ["NORTH", "SOUTH", "EAST", "WEST"], the direction "NORTH" + "SOUTH" is going north and coming back right away. The path becomes ["EAST", "WEST"], now "EAST" and "WEST" annihilate each other, therefore, the final result is []. In ["NORTH", "EAST", "WEST", "SOUTH", "WEST", "WEST"], "NORTH" and "SOUTH" are not directly opposite but they become directly opposite after the reduction of "EAST" and "WEST" so the whole path is reducible to ["WEST", "WEST"].

Not all paths can be made simpler. The path ["NORTH", "WEST", "SOUTH", "EAST"] is not reducible. "NORTH" and "WEST", "WEST" and "SOUTH", "SOUTH" and "EAST" are not directly opposite of each other and can't become such. Hence the result path is itself: ["NORTH", "WEST", "SOUTH", "EAST"].

function dirReduc(arr) {
  let x = 0;
  while (x < arr.length && arr.length > 1) {
    if (
      (arr[x] === "NORTH" && arr[x + 1] === "SOUTH") ||
      (arr[x] === "SOUTH" && arr[x + 1] === "NORTH") ||
      (arr[x] === "WEST" && arr[x + 1] === "EAST") ||
      (arr[x] === "EAST" && arr[x + 1] === "WEST")
    ) {
      arr.splice(x, 2);
      x = 0;
    } else {
      x++;
    }
  }
  return arr;
}