Lead changes

Problem

"And the lead changes hands once again," says the commentator of the volleyball match. She keeps count of those changes, and now it is your job. You get a text with the points in order, made only of uppercase A and B: each letter is one point for that team. It may be empty.

After each point, the team with more points is ahead. There is a lead change when a team goes ahead and the last team that had been ahead was the other one. The first team to go ahead does not count as a change. A tie does not count either: if after a tie the same team that was winning goes ahead again, there was no change.

Return how many changes there were, as a whole number. With "ABBAAB": A ahead, tie, B ahead (1), tie, A ahead (2), tie. You return 2.

Examples

• The example

  "ABBAAB" → 2

• A never loses the lead

  "AAABAB" → 0

• Taking the first lead is not a change

  "BBB" → 0

• The comeback

  "AAAABBBBBB" → 1

• Lots of changes

  "ABBAABBAAB" → 4

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

You start with this

def lead_changes(points):
    pass

function leadChanges(points) {
}