Problem:
Score : 100 points

Problem Statement

You are given a directed graph with N vertices and M edges, not necessarily simple. The i-th edge is oriented from the vertex a_i to the vertex b_i.
Divide this graph into strongly connected components and print them in their topological order.

Constraints

1 \leq N \leq 500,000

1 \leq M \leq 500,000

0 \leq a_i, b_i < N

Input

Input is given from Standard Input in the following format:

N M
a_0 b_0
a_1 b_1
:
a_{M - 1} b_{M - 1}

Output

Print 1+K lines, where K is the number of strongly connected components.
Print K on the first line.
Print the information of each strongly connected component in next K lines in the following format, where l is the number of vertices in the strongly connected component and v_i is the index of the vertex in it.

l v_0 v_1 ... v_{l-1}

Here, for each edge (a_i, b_i), b_i should not appear in earlier line than a_i.

If there are multiple correct output, print any of them.

Sample Input 1

6 7
1 4
5 2
3 0
5 5
4 1
0 3
4 2

Sample Output 1

4
1 5
2 4 1
1 2
2 3 0

Solution in Common Lisp (SBCL 2.0.3) (judge verdict: Accepted)

#-swank
(unless (member :child-sbcl *features*)
  (quit
   :unix-status
   (process-exit-code
    (run-program *runtime-pathname*
                 `("--control-stack-size" "256MB"
                   "--noinform" "--disable-ldb" "--lose-on-corruption" "--end-runtime-options"
                   "--eval" "(push :child-sbcl *features*)"
                   "--script" ,(namestring *load-pathname*))
                 :output t :error t :input t))))

(in-package :cl-user)
(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 (set-dispatch-macro-character #\# #\> #'cl-debug-print:debug-print-reader)

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

(defconstant +mod+ 1000000007)

(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))))

;; BEGIN_INSERTED_CONTENTS
;;;
;;; Strongly connected components of directed graph, 2-SAT
;;;

(defpackage :cp/scc
  (:use :cl)
  (:export #:scc #:scc-graph #:scc-components #:scc-sizes #:scc-count
           #:scc-p #:make-scc #:make-condensed-graph))
(in-package :cp/scc)

(defstruct (scc (:constructor %make-scc (graph components sizes count))
                (:copier nil))
  (graph nil :type vector)
  ;; components[i] := strongly connected component of the i-th vertex
  (components nil :type (simple-array (integer 0 #.most-positive-fixnum) (*)))
  ;; sizes[k] := size of the k-th strongly connected component
  (sizes nil :type (simple-array (integer 0 #.most-positive-fixnum) (*)))
  ;; the total number of strongly connected components
  (count 0 :type (integer 0 #.most-positive-fixnum)))

;; Tarjan's algorithm
;; Reference: http://www.prefield.com/algorithm/graph/strongly_connected_components.html
;; (Kosaraju's algorithm is put in the test file)
(defun make-scc (graph)
  (declare #.cl-user::opt
           (vector graph))
  (let* ((n (length graph))
         (ord 0)
         (ords (make-array n :element-type 'fixnum :initial-element -1)) ; in-order
         ;; store the lowest in-order number as the representative element of a
         ;; strongly connected component
         (lowlinks (make-array n :element-type 'fixnum))
         (components (make-array n :element-type '(integer 0 #.most-positive-fixnum)))
         (comp-index 0) ; index number of component
         (sizes (make-array n :element-type '(integer 0 #.most-positive-fixnum)
                              :initial-element 0))
         (stack (make-array n :element-type '(integer 0 #.most-positive-fixnum)))
         (end 0) ; stack pointer
         (in-stack (make-array n :element-type 'bit :initial-element 0)))
    (declare ((integer 0 #.most-positive-fixnum) ord end comp-index))
    (labels ((%push (v)
               (setf (aref stack end) v
                     (aref in-stack v) 1)
               (incf end))
             (%pop ()
               (decf end)
               (let ((v (aref stack end)))
                 (setf (aref in-stack v) 0)
                 v))
             (visit (v)
               (setf (aref ords v) ord
                     (aref lowlinks v) ord)
               (incf ord)
               (%push v)
               (dolist (next (aref graph v))
                 (cond ((= -1 (aref ords next))
                        (visit next)
                        (setf (aref lowlinks v)
                              (min (aref lowlinks v) (aref lowlinks next))))
                       ((= 1 (aref in-stack next))
                        (setf (aref lowlinks v)
                              (min (aref lowlinks v) (aref ords next))))))
               (when (= (aref lowlinks v) (aref ords v))
                 (loop for size of-type (integer 0 #.most-positive-fixnum) from 1
                       for w = (%pop)
                       do (setf (aref components w) comp-index)
                       until (= v w)
                       finally (setf (aref sizes comp-index) size)
                               (incf comp-index)))))
      (dotimes (v n)
        (when (= -1 (aref ords v))
          (visit v)))
      ;; Reverse the order of strongly connected components, because now
      ;; everything is in the reversed topological order
      (dotimes (v n)
        (setf (aref components v)
              (- comp-index (aref components v) 1)))
      (dotimes (i (ash comp-index -1))
        (rotatef (aref sizes i) (aref sizes (- comp-index i 1))))
      (%make-scc graph components sizes comp-index))))

;; FIXME: Constant factor of this implementation is too large. Can we avoid
;; hash-table?
(declaim (ftype (function * (values (simple-array t (*)) &optional))
                make-condensed-graph))
(defun make-condensed-graph (scc)
  "Does graph condensation. This function is non-destructive."
  (declare (optimize (speed 3)))
  (let* ((graph (scc-graph scc))
         (n (length graph))
         (comp-n (scc-count scc))
         (components (scc-components scc))
         (condensed (make-array comp-n :element-type t)))
    (dotimes (i comp-n)
      (setf (aref condensed i) (make-hash-table :test #'eql)))
    (dotimes (i n)
      (let ((i-comp (aref components i)))
        (dolist (neighbor (aref graph i))
          (let ((neighbor-comp (aref components neighbor)))
            (unless (= i-comp neighbor-comp)
              (setf (gethash neighbor-comp (aref condensed i-comp)) t))))))
    (dotimes (i comp-n)
      (setf (aref condensed i)
            (loop for x being each hash-key of (aref condensed i) collect x)))
    condensed))

(defpackage :cp/read-fixnum
  (:use :cl)
  (:export #:read-fixnum))
(in-package :cp/read-fixnum)

(declaim (ftype (function * (values fixnum &optional)) read-fixnum))
(defun read-fixnum (&optional (in *standard-input*))
  "NOTE: cannot read -2^62"
  (declare #.cl-user::opt)
  (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))))))))

;; BEGIN_USE_PACKAGE
(eval-when (:compile-toplevel :load-toplevel :execute)
  (use-package :cp/read-fixnum :cl-user))
(eval-when (:compile-toplevel :load-toplevel :execute)
  (use-package :cp/scc :cl-user))
(in-package :cl-user)

;;;
;;; Body
;;;

(defun main ()
  (declare #.cl-user::opt)
  (let* ((n (read))
         (m (read))
         (graph (make-array n :element-type 'list :initial-element nil)))
    (declare (uint31 n m))
    (dotimes (i m)
      (let ((a (read-fixnum))
            (b (read-fixnum)))
        (push b (aref graph a))))
    (let* ((scc (make-scc graph))
           (components (scc-components scc))
           (count (scc-count scc))
           (sizes (scc-sizes scc))
           (res (make-array count :element-type 'list :initial-element nil)))
      (dotimes (v n)
        (push v (aref res (aref components v))))
      (write-string
       (with-output-to-string (*standard-output* nil :element-type 'base-char)
         (println count)
         (dotimes (i count)
           (write (aref sizes i))
           (dolist (v (aref res i) (terpri))
             (write-char #\ )
             (write v))))))))

#-swank (main)

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

#+swank
(defun get-clipbrd ()
  (with-output-to-string (out)
    #+os-windows (run-program "powershell.exe" '("-Command" "Get-Clipboard") :output out :search t)
    #+os-unix (run-program "xsel" '("-b" "-o") :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* (or out (make-string-output-stream)))
         (res (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))))))
    (if out res (get-output-stream-string *standard-output*))))

#+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)))

#-swank
(eval-when (:compile-toplevel)
  (when (and (boundp 'sb-c::*compiler-warning-count*)
             (> sb-c::*compiler-warning-count* 0))
    (sb-ext:quit :unix-status 1)))

;; To run: (5am:run! :sample)
#+swank
(it.bese.fiveam:test :sample
  (it.bese.fiveam:is
   (equal "4
1 5
2 4 1
1 2
2 3 0
"
          (run "6 7
1 4
5 2
3 0
5 5
4 1
0 3
4 2
" nil))))