The shape of the melody

Problem

You do not need the notes to recognize a song: it is enough to know whether each one goes up, goes down or repeats. That outline is called the contour, and it is how apps find a song when you hum it.

Write a function that takes a list of note pitches, as whole numbers, and returns a string with one character for each note from the second one on, compared with the note right before it: "+" if it goes up, "-" if it goes down and "=" if it repeats.

With [60, 62, 62, 59, 64]: 62 goes up, 62 repeats, 59 goes down and 64 goes up, so you return "+=-+". The string is one shorter than the list. With a single note, or an empty list, you return the empty string "".

Examples

• The example

  [60, 62, 62, 59, 64] → "+=-+"

• Always going down

  [72, 71, 69, 67] → "---"

• The same note

  [64, 64, 64] → "=="

• Two notes

  [55, 57] → "+"

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def contour(notes):
    pass

function contour(notes) {
}