A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property CI_Cache::$apc is deprecated

Filename: libraries/Driver.php

Line Number: 188

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Cacher.php
Line: 22
Function: driver

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Cacher.php
Line: 17
Function: initiateCache

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 12
Function: __construct

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property CI_Cache::$file is deprecated

Filename: libraries/Driver.php

Line Number: 188

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Cacher.php
Line: 22
Function: driver

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Cacher.php
Line: 17
Function: initiateCache

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 12
Function: __construct

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property Contents_model::$best_cnt is deprecated

Filename: ver3/Contents_model.php

Line Number: 17

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/models/ver3/Contents_model.php
Line: 17
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 440
Function: model

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 29
Function: initMenu

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 12
Function: __construct

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property Contents_model::$popular_cnt is deprecated

Filename: ver3/Contents_model.php

Line Number: 18

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/models/ver3/Contents_model.php
Line: 18
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 440
Function: model

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 29
Function: initMenu

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 12
Function: __construct

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property Article_model::$best_cnt is deprecated

Filename: ver3/Article_model.php

Line Number: 18

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/models/ver3/Article_model.php
Line: 18
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 13
Function: model

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property Article_model::$popular_cnt is deprecated

Filename: ver3/Article_model.php

Line Number: 19

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/models/ver3/Article_model.php
Line: 19
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 13
Function: model

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: urldecode(): Passing null to parameter #1 ($string) of type string is deprecated

Filename: ver3/Member_model.php

Line Number: 279

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/models/ver3/Member_model.php
Line: 279
Function: urldecode

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 123
Function: getMemberView

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: Warning

Message: Trying to access array offset on value of type null

Filename: ver3/Article.php

Line Number: 124

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 124
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: Warning

Message: Trying to access array offset on value of type null

Filename: ver3/Article.php

Line Number: 125

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 125
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: Warning

Message: mkdir(): Permission denied

Filename: libraries/Common.php

Line Number: 202

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 202
Function: mkdir

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 236
Function: getLatexImg

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 249
Function: parseLatexImg

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 131
Function: initBoardView

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: Warning

Message: file_put_contents(/DATA/upload/polymath/latex/202f51921287058aab9d4014a0acf94c.gif): Failed to open stream: No such file or directory

Filename: libraries/Common.php

Line Number: 213

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 213
Function: file_put_contents

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/libraries/Common.php
Line: 236
Function: getLatexImg

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 249
Function: parseLatexImg

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 131
Function: initBoardView

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: 8192

Message: Creation of dynamic property CI_Cache::$dummy is deprecated

Filename: libraries/Driver.php

Line Number: 188

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/models/ver3/Article_model.php
Line: 674
Function: get

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 266
Function: getComment

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 131
Function: initBoardView

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

자유 기사 기사 작성법
일상생활 속 수학을 찾아 보세요!
[자유 기사] 사물함 자물쇠, 어떤것이 좋을까?
K→C≡N 2020.03.05 17:18

 수학동아 독자 중 이번에 중학교로 올라가는 학생들이 많을 것입니다. 이 때가 학생들이 빠르게 변하는 만큼 초등학교때와는 다르게 나쁜 일들을 좀 하는 학생들이 생기죠. 남의 사물함을 뒤져서 도둑질 하는 학생들도 자주 보입니다. 그러면 여러분은 자물쇠가 아마도 필요하실텐데요, 어떤 자물쇠가 좋을까요? 어떤 자물쇠가 좋을지 알아보기 위해 자물쇠의 종류 별로 살펴봅시다.

1.돌리는 자물쇠

사진출처: (주)자커

돌리는 자물쇠는 각 자리별로 10가지 경우의 수가 있기 때문에 세자릿수인 경우는 103=1000가지, 네자릿수인 경우는 104=10000가지가 나옵니다.

2.누르는 자물쇠

 사진출처: (주)자커

누르는 자물쇠는 각 버튼마다 2가지 경우가 있으므로 8버튼인 경우에는 28=256가지, 10버튼인 경우에는 210=1024가지가 있습니다.

이렇게까지만 보시면 '돌리는 4자리'>'누르는 10버튼'>'돌리는 3자리'>'누르는 8자리' 순으로 좋다고 할 수 있습니다.

 

하지만 경우의 수가 아닌 따는데 걸리는 시간이 오래 걸려야 좋은 자물쇠라고 할 수 있습니다.

 

돌리는 4자리인 경우, 한 칸 돌리는데 1초, 확인하는데 1초 걸린다고 가정하면 전체 경우 중 일의자리가 '9'가 아닌 나머지 90%는 돌리는데 1초, 확인하는데에 1초가 소모되고, 10n의자리가 '9'이고 10n+1의자리가 '9'가 아닌 경우는 전체의 \frac{9}{10^{n-1}}%를 차지하고, 각각 돌리는 데에 n+1초, 확인하는데에 1초가 걸리므로 총 소요시간은 2*9000+3*900+4*90+5*9=21105초가 걸립니다.

돌리는 3자리인 경우, 마찬가지로 계산을 하면 2*900+3*90+4*9=2106초가 걸립니다.

 

누르는 10자리의 경우에는 '1','2','3'이 눌러져 있고, 나머지 한 개로 나머지 수들을 누를 테니, 초기에 '1','2','3',4'을 누를 4초+일반적인 경우, 한 번 바꾸고 확인하는데 3초, 나머지는 n이상 의 수들이 모두 눌려져 있고, n-1이 눌러져 있지 않다면, 14-n초가 걸리므로 총 소요시간은 7C1*6+(8C2-7C1)*5+(9C3-8C2)*4+(10C4-9C3)*3=7*6+21*5+56*4+210*3=1001초입니다.

 

위 결과로 보면 돌리는 4자릿수가 10~20배 효과적임을 알 수 있습니다. 다른 종류에 비하여 2배정도 비싼것을 감안하여도 5~10배 더 좋은 자물쇠라고 할 수 있습니다.

 

*자물쇠를 따는 더 빠른 방법을 알고 계신분은 댓글로 소개해주세요!*

 

A PHP Error was encountered

Severity: Warning

Message: Undefined variable $tag_news_list

Filename: inc/article_view.php

Line Number: 90

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/views/ver3/inc/article_view.php
Line: 90
Function: _error_handler

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 221
Function: view

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once

A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at /volume1/web/PhpstormProjects/www_polymath_co_kr/system/core/Exceptions.php:271)

Filename: core/Common.php

Line Number: 570

Backtrace:

An uncaught Exception was encountered

Type: TypeError

Message: count(): Argument #1 ($value) must be of type Countable|array, null given

Filename: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/views/ver3/inc/article_view.php

Line Number: 90

Backtrace:

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/application/controllers/ver3/Article.php
Line: 221
Function: view

File: /volume1/web/PhpstormProjects/www_polymath_co_kr/index.php
Line: 315
Function: require_once