Now it's me.

two-simple-array-algorithms

describe('A function',function(){

  it('extracts the simmetric difference of two arrays of integers',function(){
    expect(diff([1,2,3], [4,5,6])).toEqual([1,2,3,4,5,6]);
    expect(diff([1,2,3], [1,2,3])).toEqual([]);
    expect(diff([1], [])).toEqual([1]);
    expect(diff([1], [2])).toEqual([1,2]);
    expect(diff([1,2,3], [1,2,3,4])).toEqual([4]);
  });

  it('checks if integers in an array are ordered',function(){
    expect(isOrdered([1,2,3,4,5,6])).toBe(true);
    expect(isOrdered([1])).toBe(true);
    expect(isOrdered([1,2])).toBe(true);
    expect(isOrdered([1,2,2])).toBe(true);
    expect(isOrdered([1,2,2,3])).toBe(true);

    expect(isOrdered([1,2,3,4,5,6].reverse())).toBe(true);
    expect(isOrdered([1].reverse())).toBe(true);
    expect(isOrdered([1,2].reverse())).toBe(true);
    expect(isOrdered([1,2,2].reverse())).toBe(true);
    expect(isOrdered([1,2,2,3].reverse())).toBe(true);

    expect(isOrdered([1,2,1])).toBe(false);
    expect(isOrdered([3,2,1,2])).toBe(false);
  });

});

function diff(a, b) {
  var c = a.concat(b).sort();
  var d = [];
  if (c.length === 0)
    return d;
  if (c.length == 1)
    return c;
  // Check for the first element
  if (c[0] < c[1])
    d.push(c[0]);
  if (c.length > 2) {
    // A number is unique if it's different from prev and next
    for (var i=1; i<c.length-1; i++) {
      if ((c[i-1] < c[i]) && (c[i] < c[i+1])) {
        d.push(c[i]);      
      }
    }    
  }
  // Check the last element
  if (c[c.length-2] < c[c.length-1])
    d.push(c[c.length-1]);
  
  return d;  
}

function isOrdered(a) {
  if (a.length < 2)
    return true;
  var m = 0;  
  for (var i=0; i<a.length-1; i++) {
    var x = (a[i] - a[i+1]);
    // If they're equal, loop to next element
    if (x === 0)
      continue;
    // m=0, we don't know if it's ordered up or down
    if (m === 0) {
      if (x < 0)
        m = -1;
      else if (x > 0)
        m = 1;
    }
    // Ok, check if it's ordered
    if ((x*m) < 0)
      return false;
  }
  return true;
}