// Points in 1-D
var points = [2,2,3,1,4,5];

var smallestDiff;

function mergeSort(arr) {
  if (arr.length == 1)
    return arr;

  if (arr.length > 1) {
    let breakpoint = Math.ceil((arr.length / 2));
    // Left list starts with 0, breakpoint-1
    let leftList = arr.slice(0, breakpoint);
    // Right list starts with breakpoint, length-1
    let rightList = arr.slice(breakpoint, arr.length);

    // Make a recursive call
    leftList = mergeSort(leftList);
    rightList = mergeSort(rightList);

    var a = merge(leftList, rightList);
    return a;
  }
}

function merge(leftList, rightList) {
  let result = [];
  while (leftList.length && rightList.length) {
    // Sorting the x coordinates
    if (leftList[0] <= rightList[0]) {
      result.push(leftList.shift());
    } else {
      result.push(rightList.shift());
    }
  }

  while (leftList.length)
    result.push(leftList.shift());

  while (rightList.length)
    result.push(rightList.shift());

  let diff;
  if (result.length > 1) {
    diff = result[1] - result[0];
  } else {
    diff = result[0];
  }

  if (smallestDiff) {
    if (diff < smallestDiff)
      smallestDiff = diff;
  } else {
    smallestDiff = diff;
  }
  return result;
}

mergeSort(points);

console.log(`Smallest difference: ${smallestDiff}`);