3 selection rects

CGRect firstRect = _selectionRects.count > 0 ? CGRectInset([_selectionRects.firstObject CGRectValue], -1, -1) : CGRectNull;
CGRect bigRect = CGRectNull;
CGRect lastRect = _selectionRects.count > 1 ? CGRectInset([_selectionRects.lastObject CGRectValue], -1, -1) : CGRectNull;
if (_selectionRects.count > 2) {
  for (int i = 1; i < _selectionRects.count - 1; i++) {
    NSValue *value = _selectionRects[i];
    bigRect = CGRectUnion(bigRect, CGRectInset(value.CGRectValue, -1, -1));
  }
}

if (!CGRectIsNull(bigRect)) {
  CGFloat newSize = bigRect.size.height + CGRectGetMinY(bigRect) - CGRectGetMaxY(firstRect);
  if (!CGRectIsNull(lastRect)) {
    newSize += CGRectGetMinY(lastRect) - CGRectGetMaxY(bigRect);
  }
  bigRect.origin.y = CGRectGetMaxY(firstRect);
  bigRect.size.height = newSize;
} else if (!CGRectIsNull(lastRect)) {
  // Split the difference between firstRect and lastRect
  CGFloat difference = CGRectGetMinY(lastRect) - CGRectGetMaxY(firstRect);
  CGFloat midPointY = CGRectGetMaxY(firstRect) + difference / 2.0;
  firstRect.size.height += midPointY - CGRectGetMaxY(firstRect);
  CGFloat newLastRectSize = lastRect.size.height + CGRectGetMinY(lastRect) - midPointY;
  lastRect.size.height = newLastRectSize;
  lastRect.origin.y -= difference / 2.0;
}

UIBezierPath *bezierPath = [UIBezierPath bezierPath];

BOOL displaySelectionLayer = NO;

if (!CGRectIsNull(firstRect)) {
  [bezierPath appendPath:[UIBezierPath bezierPathWithRect:firstRect]];
  displaySelectionLayer = YES;
}

if (!CGRectIsNull(bigRect)) {
  [bezierPath appendPath:[UIBezierPath bezierPathWithRect:bigRect]];
}

if (!CGRectIsNull(lastRect)) {
  [bezierPath appendPath:[UIBezierPath bezierPathWithRect:lastRect]];
}