Problem:
Score : 800 points

Problem Statement

Let N be a positive even number.

We have a permutation of (1, 2, ..., N), p = (p_1, p_2, ..., p_N).
Snuke is constructing another permutation of (1, 2, ..., N), q, following the procedure below.

First, let q be an empty sequence.
Then, perform the following operation until p becomes empty:

Select two adjacent elements in p, and call them x and y in order. Remove x and y from p (reducing the length of p by 2), and insert x and y, preserving the original order, at the beginning of q.

When p becomes empty, q will be a permutation of (1, 2, ..., N).

Find the lexicographically smallest permutation that can be obtained as q.

Constraints

N is an even number.

2 ≤ N ≤ 2 × 10^5

p is a permutation of (1, 2, ..., N).

Input

Input is given from Standard Input in the following format:

N
p_1 p_2 ... p_N

Output

Print the lexicographically smallest permutation, with spaces in between.

Sample Input 1

4
3 2 4 1

Sample Output 1

3 1 2 4

The solution above is obtained as follows:

p

q

(3, 2, 4, 1)

()

↓

↓

(3, 1)

(2, 4)

↓

↓

()

(3, 1, 2, 4)

Sample Input 2

2
1 2

Sample Output 2

1 2

Sample Input 3

8
4 6 3 2 8 5 7 1

Sample Output 3

3 1 2 7 4 6 8 5

The solution above is obtained as follows:

p

q

(4, 6, 3, 2, 8, 5, 7, 1)

()

↓

↓

(4, 6, 3, 2, 7, 1)

(8, 5)

↓

↓

(3, 2, 7, 1)

(4, 6, 8, 5)

↓

↓

(3, 1)

(2, 7, 4, 6, 8, 5)

↓

↓

()

(3, 1, 2, 7, 4, 6, 8, 5)

Solution in Common Lisp (SBCL 1.1.14) (judge verdict: Runtime Error)

(eval-when (:compile-toplevel :load-toplevel :execute)
  (sb-int:defconstant-eqx opt
    #+swank '(optimize (speed 3) (safety 2))
    #-swank '(optimize (speed 3) (safety 0) (debug 0))
    #'equal)
  #+swank (ql:quickload '(:cl-debug-print :fiveam) :silent t)
  #-swank (set-dispatch-macro-character
           #\# #\> (lambda (s c p) (declare (ignore c p)) `(values ,(read s nil nil t)))))
#+swank (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)
#-swank (disable-debugger) ; for CS Academy

(defmacro define-int-types (&rest bits)
  `(progn
     ,@(mapcar (lambda (b) `(deftype ,(intern (format nil "UINT~A" b)) () '(unsigned-byte ,b))) bits)
     ,@(mapcar (lambda (b) `(deftype ,(intern (format nil "INT~A" b)) () '(signed-byte ,b))) bits)))
(define-int-types 2 4 7 8 15 16 31 32 62 63 64)

;; BEGIN_INSERTED_CONTENTS
(declaim (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  "NOTE: cannot read -2^62"
  (macrolet ((%read-byte ()
               `(the (unsigned-byte 8)
                     #+swank (char-code (read-char in nil #\Nul))
                     #-swank (sb-impl::ansi-stream-read-byte in nil #.(char-code #\Nul) nil))))
    (let* ((minus nil)
           (result (loop (let ((byte (%read-byte)))
                           (cond ((<= 48 byte 57)
                                  (return (- byte 48)))
                                 ((zerop byte) ; #\Nul
                                  (error "Read EOF or #\Nul."))
                                 ((= byte #.(char-code #\-))
                                  (setq minus t)))))))
      (declare ((integer 0 #.most-positive-fixnum) result))
      (loop
        (let* ((byte (%read-byte)))
          (if (<= 48 byte 57)
              (setq result (+ (- byte 48)
                              (* 10 (the (integer 0 #.(floor most-positive-fixnum 10))
                                         result))))
              (return (if minus (- result) result))))))))

;;;
;;; Binary heap
;;;

(define-condition heap-empty-error (error)
  ((heap :initarg :heap :reader heap-empty-error-heap))
  (:report
   (lambda (condition stream)
     (format stream "Attempted to pop empty heap ~W" (heap-empty-error-heap condition)))))

(defmacro define-binary-heap (name &key (order '#'>) (element-type 'fixnum))
  "Defines a binary heap specialized for the given order and the element
type. This macro defines a structure of the name NAME and relevant functions:
MAKE-<NAME>, <NAME>-PUSH, <NAME>-POP, <NAME>-REINITIALIZE, <NAME>-EMPTY-P,
<NAME>-COUNT, and <NAME>-PEEK."
  (check-type name symbol)
  (let* ((string-name (string name))
         (fname-push (intern (format nil "~A-PUSH" string-name)))
         (fname-pop (intern (format nil "~A-POP" string-name)))
         (fname-reinitialize (intern (format nil "~A-REINITIALIZE" string-name)))
         (fname-empty-p (intern (format nil "~A-EMPTY-P" string-name)))
         (fname-count (intern (format nil "~A-COUNT" string-name)))
         (fname-peek (intern (format nil "~A-PEEK" string-name)))
         (fname-make (intern (format nil "MAKE-~A" string-name)))
         (acc-position (intern (format nil "~A-POSITION" string-name)))
         (acc-data (intern (format nil "~A-DATA" string-name))))
    `(progn
       (locally
           ;; prevent style warnings
           (declare #+sbcl (muffle-conditions style-warning))
         (defstruct (,name
                     (:constructor ,fname-make
                         (size
                          &aux (data ,(if (eql element-type '*)
                                          `(make-array (1+ size))
                                          `(make-array (1+ size) :element-type ',element-type))))))
           (data #() :type (simple-array ,element-type (*)))
           (position 1 :type (integer 1 #.most-positive-fixnum))))

       (declaim #+sbcl (sb-ext:maybe-inline ,fname-push))
       (defun ,fname-push (obj heap)
         "Adds OBJ to the end of HEAP."
         (declare (optimize (speed 3))
                  (type ,name heap))
         (symbol-macrolet ((position (,acc-position heap)))
           (when (>= position (length (,acc-data heap)))
             (setf (,acc-data heap)
                   (adjust-array (,acc-data heap)
                                 (min (- array-total-size-limit 1)
                                      (* position 2)))))
           (let ((data (,acc-data heap)))
             (declare ((simple-array ,element-type (*)) data))
             (labels ((update (pos)
                        (declare (optimize (speed 3) (safety 0)))
                        (unless (= pos 1)
                          (let ((parent-pos (ash pos -1)))
                            (when (funcall ,order (aref data pos) (aref data parent-pos))
                              (rotatef (aref data pos) (aref data parent-pos))
                              (update parent-pos))))))
               (setf (aref data position) obj)
               (update position)
               (incf position)
               heap))))

       (declaim #+sbcl (sb-ext:maybe-inline ,fname-pop))
       (defun ,fname-pop (heap)
         "Removes and returns the element at the top of HEAP."
         (declare (optimize (speed 3))
                  (type ,name heap))
         (symbol-macrolet ((position (,acc-position heap)))
           (let ((data (,acc-data heap)))
             (declare ((simple-array ,element-type (*)) data))
             (labels ((update (pos)
                        (declare (optimize (speed 3) (safety 0))
                                 ((integer 1 #.most-positive-fixnum) pos))
                        (let* ((child-pos1 (+ pos pos))
                               (child-pos2 (1+ child-pos1)))
                          (when (<= child-pos1 position)
                            (if (<= child-pos2 position)
                                (if (funcall ,order (aref data child-pos1) (aref data child-pos2))
                                    (unless (funcall ,order (aref data pos) (aref data child-pos1))
                                      (rotatef (aref data pos) (aref data child-pos1))
                                      (update child-pos1))
                                    (unless (funcall ,order (aref data pos) (aref data child-pos2))
                                      (rotatef (aref data pos) (aref data child-pos2))
                                      (update child-pos2)))
                                (unless (funcall ,order (aref data pos) (aref data child-pos1))
                                  (rotatef (aref data pos) (aref data child-pos1))))))))
               (when (= position 1)
                 (error 'heap-empty-error :heap heap))
               (prog1 (aref data 1)
                 (decf position)
                 (setf (aref data 1) (aref data position))
                 (update 1))))))

       (declaim (inline ,fname-reinitialize))
       (defun ,fname-reinitialize (heap)
         "Makes HEAP empty."
         (setf (,acc-position heap) 1)
         heap)

       (declaim (inline ,fname-empty-p))
       (defun ,fname-empty-p (heap)
         "Returns true iff HEAP is empty."
         (= 1 (,acc-position heap)))

       (declaim (inline ,fname-count))
       (defun ,fname-count (heap)
         "Returns the current number of the elements in HEAP."
         (- (,acc-position heap) 1))

       (declaim (inline ,fname-peek))
       (defun ,fname-peek (heap)
         "Returns the topmost element of HEAP."
         (if (= 1 (,acc-position heap))
             (error 'heap-empty-error :heap heap)
             (aref (,acc-data heap) 1))))))

;;;
;;; Disjoint sparse table on arbitrary semigroup
;;;

;;; Reference:
;;; https://discuss.codechef.com/questions/117696/tutorial-disjoint-sparse-table
;;; http://noshi91.hatenablog.com/entry/2018/05/08/183946 (Japanese)
;;; http://drken1215.hatenablog.com/entry/2018/09/08/162600 (Japanese)

;; NOTE: This constructor is slow on SBCL version earlier than 1.5.6 as the type
;; propagation of MAKE-ARRAY doesn't work. The following files are required to
;; enable the optimization.
;; version < 1.5.0: array-element-type.lisp, make-array-header.lisp
;; version < 1.5.6: make-array-header.lisp
(declaim (inline make-disjoint-sparse-table))
(defun make-disjoint-sparse-table (vector binop)
  "BINOP := binary operator (comprising a semigroup)"
  (declare ((simple-array uint32 (*)) vector))
  (let* ((n (length vector))
         (height (max 1 (integer-length (- n 1))))
         (table (make-array (list height n) :element-type 'uint32)))
    (dotimes (j n)
      (setf (aref table 0 j) (aref vector j)))
    (do ((i 1 (+ i 1)))
        ((>= i height))
      (let* ((width/2 (ash 1 i))
             (width (* width/2 2)))
        (do ((j 0 (+ j width)))
            ((>= j n))
          (let ((mid (min (+ j width/2) n)))
            ;; fill the first half
            (setf (aref table i (- mid 1))
                  (aref vector (- mid 1)))
            (do ((k (- mid 2) (- k 1)))
                ((< k j))
              (setf (aref table i k)
                    (funcall binop (aref vector k) (aref table i (+ k 1)))))
            (when (>= mid n)
              (return))
            ;; fill the second half
            (setf (aref table i mid)
                  (aref vector mid))
            (let ((end (min n (+ mid width/2))))
              (do ((k (+ mid 1) (+ k 1)))
                  ((>= k end))
                (setf (aref table i k)
                      (funcall binop (aref table i (- k 1)) (aref vector k)))))))))
    table))

(declaim (inline dst-query))
(defun dst-query (table binop left right &optional identity)
  "Queries the interval [LEFT, RIGHT). Returns IDENTITY for a null interval [x,
x)."
  (declare ((integer 0 #.most-positive-fixnum) left right)
           ((simple-array * (* *)) table))
  (when (>= left right)
    (assert (= left right))
    (return-from dst-query identity))
  (setq right (- right 1)) ;; change to closed interval
  (if (= left right)
      (aref table 0 left)
      (let ((h (- (integer-length (logxor left right)) 1)))
        (funcall binop
                 (aref table h left)
                 (aref table h right)))))

(defmacro dbg (&rest forms)
  #+swank
  (if (= (length forms) 1)
      `(format *error-output* "~A => ~A~%" ',(car forms) ,(car forms))
      `(format *error-output* "~A => ~A~%" ',forms `(,,@forms)))
  #-swank (declare (ignore forms)))

(declaim (inline println))
(defun println (obj &optional (stream *standard-output*))
  (let ((*read-default-float-format* 'double-float))
    (prog1 (princ obj stream) (terpri stream))))

(defconstant +mod+ 1000000007)

;;;
;;; Body
;;;

;; min l . r
(define-binary-heap heap
  :order (lambda (node1 node2)
           (< (the fixnum (car node1))
              (the fixnum (car node2))))
  :element-type list)

(defconstant +inf+ #xffffffff)

(defun main ()
  (let* ((n (read))
         (ps (make-array n :element-type 'uint32 :initial-element 0))
         (invs (make-array n :element-type 'uint32 :initial-element 0))
         (odd-ps (make-array n :element-type 'uint32 :initial-element 0))
         (even-ps (make-array n :element-type 'uint32 :initial-element 0)))
    (dotimes (i n)
      (let ((p (- (read-fixnum) 1)))
        (setf (aref ps i) p
              (aref invs p) i
              (aref even-ps i) (if (evenp i) p +inf+)
              (aref odd-ps i) (if (oddp i) p +inf+))))
    (let ((odd-table (make-disjoint-sparse-table odd-ps #'min))
          (even-table (make-disjoint-sparse-table even-ps #'min))
          (min-table (make-disjoint-sparse-table ps #'min))
          (que (make-heap n))
          res)
      #>invs
      (heap-push (list* (dst-query even-table #'min 0 (- n 1)) 0 n) que)
      (loop until (heap-empty-p que)
            for (min1 l . r) = (heap-pop que)
            for min1-pos = (aref invs min1)
            for min2 = (if (evenp min1-pos)
                           (dst-query odd-table #'min (+ 1 min1-pos) r)
                           (dst-query even-table #'min (+ 1 min1-pos) r))
            for min2-pos = (aref invs min2)
            do (push (+ min1 1) res)
               (push (+ min2 1) res)
               (dbg l r min1 min1-pos min2 min2-pos)
               (assert (and (<= l min1-pos)
                            (< min1-pos min2-pos)
                            (< min2-pos r)))
               (when (< l min1-pos)
                 (assert (evenp (- min1-pos l)))
                 (dbg l min1-pos)
                 (heap-push (list* (dst-query min-table #'min l (- min1-pos 1))
                                   l min1-pos)
                            que))
               (when (< (+ min1-pos 1) min2-pos)
                 (assert (evenp (- min2-pos (+ min1-pos 1))))
                 (dbg (+ min1-pos 1) min2-pos)
                 (heap-push (list* (dst-query min-table #'min (+ min1-pos 1) (- min2-pos 1))
                                   (+ min1-pos 1) min2-pos)
                            que))
               (when (< (+ min2-pos 1) r)
                 (assert (evenp (- r (+ min2-pos 1))))
                 (dbg (+ min2-pos 1) r)
                 (heap-push (list* (dst-query min-table #'min (+ min2-pos 1) (- r 1))
                                   (+ min2-pos 1) r)
                            que)))
      (write-string
       (with-output-to-string (*standard-output* nil :element-type 'base-char)
         (format t "~{~D~^ ~}~%" (reverse res)))))))

#-swank (main)

;;;
;;; Test and benchmark
;;;

#+swank
(defun io-equal (in-string out-string &key (function #'main) (test #'equal))
  "Passes IN-STRING to *STANDARD-INPUT*, executes FUNCTION, and returns true if
the string output to *STANDARD-OUTPUT* is equal to OUT-STRING."
  (labels ((ensure-last-lf (s)
             (if (eql (uiop:last-char s) #\Linefeed)
                 s
                 (uiop:strcat s uiop:+lf+))))
    (funcall test
             (ensure-last-lf out-string)
             (with-output-to-string (out)
               (let ((*standard-output* out))
                 (with-input-from-string (*standard-input* (ensure-last-lf in-string))
                   (funcall function)))))))

#+swank
(defun get-clipbrd ()
  (with-output-to-string (out)
    (run-program "powershell.exe" '("-Command" "Get-Clipboard") :output out :search t)))

#+swank (defparameter *this-pathname* (uiop:current-lisp-file-pathname))
#+swank (defparameter *dat-pathname* (uiop:merge-pathnames* "test.dat" *this-pathname*))

#+swank
(defun run (&optional thing (out *standard-output*))
  "THING := null | string | symbol | pathname

null: run #'MAIN using the text on clipboard as input.
string: run #'MAIN using the string as input.
symbol: alias of FIVEAM:RUN!.
pathname: run #'MAIN using the text file as input."
  (let ((*standard-output* out))
    (etypecase thing
      (null
       (with-input-from-string (*standard-input* (delete #\Return (get-clipbrd)))
         (main)))
      (string
       (with-input-from-string (*standard-input* (delete #\Return thing))
         (main)))
      (symbol (5am:run! thing))
      (pathname
       (with-open-file (*standard-input* thing)
         (main))))))

#+swank
(defun gen-dat ()
  (uiop:with-output-file (out *dat-pathname* :if-exists :supersede)
    (format out "")))

#+swank
(defun bench (&optional (out (make-broadcast-stream)))
  (time (run *dat-pathname* out)))

;; To run: (5am:run! :sample)
#+swank
(it.bese.fiveam:test :sample
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "4
3 2 4 1
"
    "3 1 2 4
"))
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "2
1 2
"
    "1 2
"))
  (it.bese.fiveam:is
   (common-lisp-user::io-equal "8
4 6 3 2 8 5 7 1
"
    "3 1 2 7 4 6 8 5
")))