Problem:
Score : 600 points

Problem Statement

There is a grid of squares with H+1 horizontal rows and W vertical columns.

You will start at one of the squares in the top row and repeat moving one square right or down. However, for each integer i from 1 through H, you cannot move down from the A_i-th, (A_i + 1)-th, \ldots, B_i-th squares from the left in the i-th row from the top.

For each integer k from 1 through H, find the minimum number of moves needed to reach one of the squares in the (k+1)-th row from the top. (The starting square can be chosen individually for each case.) If, starting from any square in the top row, none of the squares in the (k+1)-th row can be reached, print -1 instead.

Constraints

1 \leq H,W \leq 2\times 10^5

1 \leq A_i \leq B_i \leq W

Input

Input is given from Standard Input in the following format:

H W
A_1 B_1
A_2 B_2
:
A_H B_H

Output

Print H lines. The i-th line should contain the answer for the case k=i.

Sample Input 1

4 4
2 4
1 1
2 3
2 4

Sample Output 1

1
3
6
-1

Let (i,j) denote the square at the i-th row from the top and j-th column from the left.

For k=1, we need one move such as (1,1) → (2,1).

For k=2, we need three moves such as (1,1) → (2,1) → (2,2) → (3,2).

For k=3, we need six moves such as (1,1) → (2,1) → (2,2) → (3,2) → (3,3) → (3,4) → (4,4).

For k=4, it is impossible to reach any square in the fifth row from the top.

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

(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 (cl-syntax:use-syntax cl-debug-print:debug-print-syntax)

(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)

(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


(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))))))))

(defpackage :cp/modify-macro
  (:use :cl)
  (:export #:minf #:maxf #:mulf #:divf #:iorf #:xorf #:andf))
(in-package :cp/modify-macro)

(macrolet ((def (name fname)
             `(define-modify-macro ,name (new-value) ,fname)))
  (def minf min)
  (def maxf max)
  (def mulf *)
  (def divf /)
  (def iorf logior)
  (def xorf logxor)
  (def andf logand))

;;;
;;; Treap with explicit key
;;; Virtually it works like std::map, std::multiset, or java.util.TreeMap.
;;;

(defpackage :cp/explicit-treap
  (:use :cl)
  (:export #:treap #:treap-p #:treap-key #:treap-accumulator
           #:treap-split #:treap-insert #:treap-merge #:treap-delete
           #:treap-ensure-key #:treap-unite #:treap-map #:do-treap
           #:make-treap #:treap-fold #:treap-update #:treap-ref
           #:treap-first #:treap-last #:treap-find
           #:treap-bisect-left #:treap-bisect-right #:treap-bisect-left-1 #:treap-bisect-right-1
           #:treap-fold-bisect #:treap-fold-bisect-from-end))
(in-package :cp/explicit-treap)

;; Tips to use this structure as a multiset: Just define OP as (defun op (x y)
;; (+ x y)) and insert each element by
;;
;; (treap-ensure-key <treap> <key> 1 :if-exists #'1+)
;;
;; instead of TREAP-INSERT.

;; TODO & NOTE: insufficient tests
;; TODO: introduce abstraction by macro

(declaim (inline op))
(defun op (x y)
  "Is the operator comprising a monoid"
  (declare ((integer 0 #.most-positive-fixnum) x y))
  (min x y))

(defconstant +op-identity+ most-positive-fixnum
  "identity element w.r.t. OP")

(defstruct (treap (:constructor %make-treap (key priority value &key left right (accumulator value)))
                  (:copier nil)
                  (:conc-name %treap-))
  (key 0 :type fixnum)
  (value +op-identity+ :type fixnum)
  (accumulator +op-identity+ :type fixnum)
  (priority 0 :type (integer 0 #.most-positive-fixnum))
  (left nil :type (or null treap))
  (right nil :type (or null treap)))

(declaim (inline treap-key))
(defun treap-key (treap)
  "Returns the key of the (nullable) TREAP."
  (and treap (%treap-key treap)))

(declaim (inline treap-accumulator))
(defun treap-accumulator (treap)
  (declare ((or null treap) treap))
  (if (null treap)
      +op-identity+
      (%treap-accumulator treap)))

(declaim (inline update-accumulator))
(defun update-accumulator (treap)
  (declare (treap treap))
  (setf (%treap-accumulator treap)
        (if (%treap-left treap)
            (if (%treap-right treap)
                (let ((mid-res (op (%treap-accumulator (%treap-left treap))
                                   (%treap-value treap))))
                  (op mid-res (%treap-accumulator (%treap-right treap))))
                (op (%treap-accumulator (%treap-left treap))
                    (%treap-value treap)))
            (if (%treap-right treap)
                (op (%treap-value treap)
                    (%treap-accumulator (%treap-right treap)))
                (%treap-value treap)))))

(declaim (inline force-up))
(defun force-up (treap)
  "Propagates up the information from children."
  (declare (treap treap))
  (update-accumulator treap))

(declaim (ftype (function * (values (or null treap) (or null treap) &optional)) treap-split))
(defun treap-split (treap key &key (order #'<))
  "Destructively splits the TREAP with reference to KEY and returns two treaps,
the smaller sub-treap (< KEY) and the larger one (>= KEY)."
  (declare #.cl-user::opt
           (function order)
           ((or null treap) treap))
  (if (null treap)
      (values nil nil)
      (progn
        (if (funcall order (%treap-key treap) key)
            (multiple-value-bind (left right)
                (treap-split (%treap-right treap) key :order order)
              (setf (%treap-right treap) left)
              (force-up treap)
              (values treap right))
            (multiple-value-bind (left right)
                (treap-split (%treap-left treap) key :order order)
              (setf (%treap-left treap) right)
              (force-up treap)
              (values left treap))))))

(declaim (inline treap-insert))
(defun treap-insert (treap key value &key (order #'<))
  "Destructively inserts KEY into TREAP and returns the resultant treap. You
cannot rely on the side effect. Use the returned value.

The behavior is undefined when duplicate keys are inserted."
  (declare ((or null treap) treap)
           (function order))
  (labels ((recur (node treap)
             (declare (treap node))
             (unless treap (return-from recur node))
             (if (> (%treap-priority node) (%treap-priority treap))
                 (progn
                   (setf (values (%treap-left node) (%treap-right node))
                         (treap-split treap (%treap-key node) :order order))
                   (force-up node)
                   node)
                 (progn
                   (if (funcall order (%treap-key node) (%treap-key treap))
                       (setf (%treap-left treap)
                             (recur node (%treap-left treap)))
                       (setf (%treap-right treap)
                             (recur node (%treap-right treap))))
                   (force-up treap)
                   treap))))
    (recur (%make-treap key (random most-positive-fixnum) value) treap)))

(declaim (inline treap-ensure-key))
(defun treap-ensure-key (treap key value &key (order #'<) if-exists)
  "IF-EXISTS := nil | function

Ensures that TREAP contains KEY and assigns VALUE to it if IF-EXISTS is
false. If IF-EXISTS is function and TREAP already contains KEY, TREAP-ENSURE-KEY
updates the value by the function instead of overwriting it with VALUE."
  (declare (function order)
           ((or null treap) treap))
  (labels ((find-and-update (treap)
             ;; Updates the value slot and returns T if KEY exists
             (unless treap (return-from find-and-update nil))
             (cond ((funcall order key (%treap-key treap))
                    (when (find-and-update (%treap-left treap))
                      (force-up treap)
                      t))
                   ((funcall order (%treap-key treap) key)
                    (when (find-and-update (%treap-right treap))
                      (force-up treap)
                      t))
                   (t (setf (%treap-value treap)
                            (if if-exists
                                (funcall if-exists (%treap-value treap))
                                value))
                      (force-up treap)
                      t))))
    (if (find-and-update treap)
        treap
        (treap-insert treap key value :order order))))

(defun treap-merge (left right)
  "Destructively concatenates two treaps. Assumes that all keys of LEFT are
smaller (or larger, depending on the order) than those of RIGHT.

Note that this `merge' is different from CL:MERGE and rather close to
CL:CONCATENATE."
  (declare #.cl-user::opt
           ((or null treap) left right))
  (cond ((null left) (when right (force-up right)) right)
        ((null right) (when left (force-up left)) left)
        (t
         (if (> (%treap-priority left) (%treap-priority right))
             (progn
               (setf (%treap-right left)
                     (treap-merge (%treap-right left) right))
               (force-up left)
               left)
             (progn
               (setf (%treap-left right)
                     (treap-merge left (%treap-left right)))
               (force-up right)
               right)))))

(defun treap-delete (treap key &key (order #'<))
  "Destructively deletes the KEY in TREAP and returns the resultant
treap. Returns the unmodified TREAP If KEY doesn't exist. You cannot rely on the
side effect. Use the returned value.

 (Note that this function deletes at most one node even if duplicated keys
exist.)"
  (declare ((or null treap) treap)
           (function order))
  (when treap
    (cond ((funcall order key (%treap-key treap))
           (setf (%treap-left treap)
                 (treap-delete (%treap-left treap) key :order order))
           (force-up treap)
           treap)
          ((funcall order (%treap-key treap) key)
           (setf (%treap-right treap)
                 (treap-delete (%treap-right treap) key :order order))
           (force-up treap)
           treap)
          (t
           (treap-merge (%treap-left treap) (%treap-right treap))))))

(declaim (inline treap-unite))
(defun treap-unite (treap1 treap2 &key (order #'<))
  "Merges two treaps with keeping the order."
  (labels
      ((recur (l r)
         (cond ((null l) (when r (force-up r)) r)
               ((null r) (when l (force-up l)) l)
               (t (when (< (%treap-priority l) (%treap-priority r))
                    (rotatef l r))
                  (multiple-value-bind (lchild rchild)
                      (treap-split r (%treap-key l) :order order)
                    (setf (%treap-left l) (recur (%treap-left l) lchild)
                          (%treap-right l) (recur (%treap-right l) rchild))
                    (force-up l)
                    l)))))
    (recur treap1 treap2)))

(declaim (inline treap-map))
(defun treap-map (function treap)
  "Successively applies FUNCTION to TREAP[0], ..., TREAP[SIZE-1]. FUNCTION must
take two arguments: KEY and VALUE."
  (labels ((recur (treap)
             (when treap
               (recur (%treap-left treap))
               (funcall function (%treap-key treap) (%treap-value treap))
               (recur (%treap-right treap))
               (force-up treap))))
    (recur treap)))

(defmethod print-object ((object treap) stream)
  (print-unreadable-object (object stream :type t)
    (let ((init t))
      (treap-map (lambda (key value)
                   (if init
                       (setf init nil)
                       (write-char #\  stream))
                   (format stream "<~A . ~A>" key value))
                 object))))

(defmacro do-treap ((key-var value-var treap &optional result) &body body)
  "Successively binds the key and value of INODE[0], ..., INODE[SIZE-1] to
KEY-VAR and VALUE-VAR and executes BODY."
  `(block nil
     (treap-map (lambda (,key-var ,value-var) ,@body) ,treap)
     ,result))

;; This function takes O(nlog(n)) time. It is just for debugging.
(defun treap (order &rest key-and-values)
  "Takes cons cells in the form of (<key> . <value>)."
  (loop with res = nil
        for (key . value) in key-and-values
        do (setf res (treap-insert res key value :order order))
        finally (return res)))

;; Reference: https://cp-algorithms.com/data_structures/treap.html
;; TODO: take a sorted list as the argument
(declaim (inline make-treap))
(defun make-treap (sorted-vector)
  "Makes a treap using each key of the given SORTED-VECTOR in O(n) time. Note
that this function doesn't check if the SORTED-VECTOR is actually sorted
w.r.t. your intended order. The values are filled with the identity element."
  (declare (vector sorted-vector))
  (labels ((heapify (top)
             (when top
               (let ((prioritized-node top))
                 (when (and (%treap-left top)
                            (> (%treap-priority (%treap-left top))
                               (%treap-priority prioritized-node)))
                   (setq prioritized-node (%treap-left top)))
                 (when (and (%treap-right top)
                            (> (%treap-priority (%treap-right top))
                               (%treap-priority prioritized-node)))
                   (setq prioritized-node (%treap-right top)))
                 (unless (eql prioritized-node top)
                   (rotatef (%treap-priority prioritized-node)
                            (%treap-priority top))
                   (heapify prioritized-node)))))
           (build (l r)
             (declare ((integer 0 #.most-positive-fixnum) l r))
             (if (= l r)
                 nil
                 (let* ((mid (ash (+ l r) -1))
                        (node (%make-treap (aref sorted-vector mid)
                                           (random most-positive-fixnum)
                                           +op-identity+)))
                   (setf (%treap-left node) (build l mid))
                   (setf (%treap-right node) (build (+ mid 1) r))
                   (heapify node)
                   node))))
    (build 0 (length sorted-vector))))

(declaim (inline treap-ref))
(defun treap-ref (treap key &key (order #'<))
  (declare ((or null treap) treap))
  (labels ((recur (treap)
             (when treap
               (prog1 (cond ((funcall order key (%treap-key treap))
                             (recur (%treap-left treap)))
                            ((funcall order (%treap-key treap) key)
                             (recur (%treap-right treap)))
                            (t (%treap-value treap)))
                 (force-up treap)))))
    (recur treap)))

(declaim (inline (setf treap-ref)))
(defun (setf treap-ref) (new-value treap key &key (order #'<))
  (declare ((or null treap) treap))
  (labels ((recur (treap)
             (when treap
               (prog1 (cond ((funcall order key (%treap-key treap))
                             (recur (%treap-left treap)))
                            ((funcall order (%treap-key treap) key)
                             (recur (%treap-right treap)))
                            (t (setf (%treap-value treap) new-value)))
                 (force-up treap)))))
    (recur treap)))

(defun treap-first (treap)
  (declare (optimize (speed 3))
           (treap treap))
  (if (%treap-left treap)
      (treap-first (%treap-left treap))
      (%treap-key treap)))

(defun treap-last (treap)
  (declare (optimize (speed 3))
           (treap treap))
  (if (%treap-right treap)
      (treap-last (%treap-right treap))
      (%treap-key treap)))

;;;
;;; Bisection search w.r.t. key
;;;

;; NOTE: These functions intentionally don't return the assigned value. That is
;; for efficiency, because thereby they don't need to execute lazy propagation.

(defun treap-find (treap key &key (order #'<))
  "Finds the key that satisfies (AND (NOT (FUNCALL ORDER KEY (%TREAP-KEY
<sub-treap>))) (NOT (FUNCALL ORDER (%TREAP-KEY <sub-treap>) KEY))) and returns
KEY if it exists, otherwise returns NIL."
  (declare (optimize (speed 3))
           (function order)
           ((or null treap) treap))
  (cond ((null treap) nil)
        ((funcall order key (%treap-key treap))
         (treap-find (%treap-left treap) key :order order))
        ((funcall order (%treap-key treap) key)
         (treap-find (%treap-right treap) key :order order))
        (t key)))

(declaim (inline treap-bisect-left))
(defun treap-bisect-left (treap key &key (order #'<))
  "Returns the smallest key equal to or larger than KEY. Returns NIL if KEY is
larger than any keys in TREAP."
  (declare ((or null treap) treap)
           (function order))
  (labels ((recur (treap)
             (unless treap (return-from recur nil))
             (if (funcall order (%treap-key treap) key)
                 (recur (%treap-right treap))
                 (or (recur (%treap-left treap))
                     treap))))
    (treap-key (recur treap))))

(declaim (inline treap-bisect-left))
(defun treap-bisect-right (treap key &key (order #'<))
  "Returns the smallest key larger than KEY. Returns NIL if KEY is equal to or
larger than any keys in TREAP."
  (declare ((or null treap) treap)
           (function order))
  (labels ((recur (treap)
             (unless treap (return-from recur nil))
             (if (funcall order key (%treap-key treap))
                 (or (recur (%treap-left treap))
                     treap)
                 (recur (%treap-right treap)))))
    (treap-key (recur treap))))

(declaim (inline treap-bisect-left-1))
(defun treap-bisect-left-1 (treap key &key (order #'<))
  "Returns the largest key smaller than KEY. Returns NIL if KEY is equal to or
smaller than any keys in TREAP."
  (declare ((or null treap) treap)
           (function order))
  (labels ((recur (treap)
             (unless treap (return-from recur nil))
             (if (funcall order (%treap-key treap) key)
                 (or (recur (%treap-right treap))
                     treap)
                 (recur (%treap-left treap)))))
    (treap-key (recur treap))))

(declaim (inline treap-bisect-right-1))
(defun treap-bisect-right-1 (treap key &key (order #'<))
  "Returns the largest key equal to or smaller than KEY. Returns NIL if KEY is
smaller than any keys in TREAP."
  (declare ((or null treap) treap)
           (function order))
  (labels ((recur (treap)
             (unless treap (return-from recur nil))
             (if (funcall order key (%treap-key treap))
                 (recur (%treap-left treap))
                 (or (recur (%treap-right treap))
                     treap))))
    (treap-key (recur treap))))

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

;;;
;;; Body
;;;

(defun main ()
  (declare #.cl-user::opt)
  (let* ((h (read))
         (w (read))
         treap)
    (declare (uint31 h w))
    (dotimes (i w)
      (setq treap (treap-insert treap i 0)))
    (write-string
     (with-output-to-string (*standard-output* nil :element-type 'base-char)
       (dotimes (i h)
         (let ((a (- (read-fixnum) 1))
               (b (read-fixnum))
               (hi-dist most-positive-fixnum))
           (declare (uint62 hi-dist))
           (multiple-value-bind (treap-left treap-rest) (treap-split treap a)
             (multiple-value-bind (treap-mid treap-right) (treap-split treap-rest b)
               (treap-map (lambda (col cumul)
                            (let ((hi-delta (- b col)))
                              (minf hi-dist (+ cumul hi-delta))))
                          treap-mid)
               (setq treap (treap-merge treap-left treap-right))
               (when (and (< b w) (< hi-dist most-positive-fixnum))
                 (setq treap (treap-ensure-key
                              treap b hi-dist
                              :if-exists (lambda (value) (min value hi-dist)))))))
           (let ((res (treap-accumulator treap)))
             (println (if (>= res most-positive-fixnum)
                          -1
                          (+ i 1 res))))))))))

#-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)))

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