(defun equi-leader (a)
  (let ((vec (coerce a 'vector))
        (leader-size 0) (value 0))
    (loop for v across vec
          do (cond
               ((zerop leader-size) (incf leader-size) (setf value v))
               ((/= value v) (decf leader-size))
               (t (incf leader-size))))
    (let* ((candidate (if (> leader-size 0) value -1))
           (leader-count 0))
      (loop for v across vec do (when (= v candidate) (incf leader-count)))
      (let ((leader (if (> leader-count (/ (length vec) 2)) candidate -1))
            (count (length vec))
            (l-leader-count 0)
            (equi-leaders 0))
        (loop for k from 0 below count
              for v = (aref vec k)
              do (let ((left-half (floor (1+ k) 2))
                       (right-half (floor (- count k 1) 2)))
                   (when (= v leader) (incf l-leader-count))
                   (let ((r-leader-count (- leader-count l-leader-count)))
                     (when (and (> l-leader-count left-half)
                                (> r-leader-count right-half))
                       (incf equi-leaders)))))
        equi-leaders))))