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[essaysir] WEEK 02 Solutions#2681

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[essaysir] WEEK 02 Solutions#2681
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@essaysir

@essaysir essaysir commented Jun 29, 2026

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๋‹ต์•ˆ ์ œ์ถœ ๋ฌธ์ œ

์ž‘์„ฑ์ž ์ฒดํฌ ๋ฆฌ์ŠคํŠธ

  • Projects์˜ ์˜ค๋ฅธ์ชฝ ๋ฒ„ํŠผ(โ–ผ)์„ ๋ˆŒ๋Ÿฌ ํ™•์žฅํ•œ ๋’ค, Week๋ฅผ ํ˜„์žฌ ์ฃผ์ฐจ๋กœ ์„ค์ •ํ•ด์ฃผ์„ธ์š”.
  • ๋ฌธ์ œ๋ฅผ ๋ชจ๋‘ ํ‘ธ์‹œ๋ฉด ํ”„๋กœ์ ํŠธ์—์„œ Status๋ฅผ In Review๋กœ ์„ค์ •ํ•ด์ฃผ์„ธ์š”.
  • ์ฝ”๋“œ ๊ฒ€ํ† ์ž 1๋ถ„ ์ด์ƒ์œผ๋กœ๋ถ€ํ„ฐ ์Šน์ธ์„ ๋ฐ›์œผ์…จ๋‹ค๋ฉด PR์„ ๋ณ‘ํ•ฉํ•ด์ฃผ์„ธ์š”.

๊ฒ€ํ† ์ž ์ฒดํฌ ๋ฆฌ์ŠคํŠธ

Important

๋ณธ์ธ ๋‹ต์•ˆ ์ œ์ถœ ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ ๋‹ค๋ฅธ ๋ถ„ PR ํ•˜๋‚˜ ์ด์ƒ์„ ๋ฐ˜๋“œ์‹œ ๊ฒ€ํ† ๋ฅผ ํ•ด์ฃผ์…”์•ผ ํ•ฉ๋‹ˆ๋‹ค!

  • ๋ฐ”๋กœ ์ด์ „์— ์˜ฌ๋ผ์˜จ PR์— ๋ณธ์ธ์„ ์ฝ”๋“œ ๋ฆฌ๋ทฐ์–ด๋กœ ์ถ”๊ฐ€ํ•ด์ฃผ์„ธ์š”.
  • ๋ณธ์ธ์ด ๊ฒ€ํ† ํ•ด์•ผํ•˜๋Š” PR์˜ ๋‹ต์•ˆ ์ฝ”๋“œ์— ํ”ผ๋“œ๋ฐฑ์„ ์ฃผ์„ธ์š”.
  • ํ† ์š”์ผ ์ „๊นŒ์ง€ PR์„ ๋ณ‘ํ•ฉํ•  ์ˆ˜ ์žˆ๋„๋ก ์Šน์ธํ•ด์ฃผ์„ธ์š”.

@dalestudy

dalestudy Bot commented Jun 29, 2026

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๐Ÿ“Š essaysir ๋‹˜์˜ ํ•™์Šต ํ˜„ํ™ฉ

์ด๋ฒˆ ์ฃผ ์ œ์ถœ ๋ฌธ์ œ

๋ฌธ์ œ ๋‚œ์ด๋„ ์œ ํ˜• ๋ถ„์„
3sum Medium โš ๏ธ ์œ ํ˜• ๋ถˆ์ผ์น˜
climbing-stairs Easy โœ… ์˜๋„ํ•œ ์œ ํ˜•
product-of-array-except-self Medium โš ๏ธ ์œ ํ˜• ๋ถˆ์ผ์น˜
valid-anagram Easy โœ… ์˜๋„ํ•œ ์œ ํ˜•
validate-binary-search-tree Medium โœ… ์˜๋„ํ•œ ์œ ํ˜•

๋ˆ„์  ํ•™์Šต ์š”์•ฝ

  • ํ’€์ดํ•œ ๋ฌธ์ œ: 5 / 75๊ฐœ
  • ์ด๋ฒˆ ์ฃผ ์œ ํ˜• ์ผ์น˜์œจ: 60% (5๋ฌธ์ œ ์ค‘ 3๋ฌธ์ œ ์ผ์น˜)

๋ฌธ์ œ ํ’€์ด ํ˜„ํ™ฉ

์นดํ…Œ๊ณ ๋ฆฌ ์ง„ํ–‰๋„ ์™„๋ฃŒ
Heap โ– โ– โ–กโ–กโ–กโ–กโ–ก 1 / 3 (Medium 1)
Array โ– โ–กโ–กโ–กโ–กโ–กโ–ก 2 / 10 (Easy 2)
Graph โ– โ–กโ–กโ–กโ–กโ–กโ–ก 1 / 8 (Medium 1)
Dynamic Programming โ– โ–กโ–กโ–กโ–กโ–กโ–ก 1 / 11 (Medium 1)
Binary โ–กโ–กโ–กโ–กโ–กโ–กโ–ก 0 / 5 โ† ์•„์ง ์‹œ์ž‘ ์•ˆ ํ•จ
Interval โ–กโ–กโ–กโ–กโ–กโ–กโ–ก 0 / 5 โ† ์•„์ง ์‹œ์ž‘ ์•ˆ ํ•จ
Linked List โ–กโ–กโ–กโ–กโ–กโ–กโ–ก 0 / 6 โ† ์•„์ง ์‹œ์ž‘ ์•ˆ ํ•จ
Matrix โ–กโ–กโ–กโ–กโ–กโ–กโ–ก 0 / 4 โ† ์•„์ง ์‹œ์ž‘ ์•ˆ ํ•จ
String โ–กโ–กโ–กโ–กโ–กโ–กโ–ก 0 / 10 โ† ์•„์ง ์‹œ์ž‘ ์•ˆ ํ•จ
Tree โ–กโ–กโ–กโ–กโ–กโ–กโ–ก 0 / 14 โ† ์•„์ง ์‹œ์ž‘ ์•ˆ ํ•จ

๐Ÿค– ์ด ๋Œ“๊ธ€์€ GitHub App์„ ํ†ตํ•ด ์ž๋™์œผ๋กœ ์ž‘์„ฑ๋˜์—ˆ์Šต๋‹ˆ๋‹ค.

๐Ÿ”ข API ์‚ฌ์šฉ๋Ÿ‰ (gpt-5-nano)
์š”์ฒญ ์ž…๋ ฅ ํ† ํฐ ์ถœ๋ ฅ ํ† ํฐ ํ•ฉ๊ณ„ ๋น„์šฉ
1 754 116 870 $0.000084
2 793 119 912 $0.000087
3 1,267 111 1,378 $0.000108
4 1,267 111 1,378 $0.000108
5 2,148 262 2,410 $0.000212
6 2,148 250 2,398 $0.000207
ํ•ฉ๊ณ„ 8,377 969 9,346 $0.000806

@github-actions github-actions Bot added the java label Jun 29, 2026

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์ œ ์ƒ๊ฐ์— dfs ํ•จ์ˆ˜์— ์ ์ ˆํ•œ cache๋งŒ ์ถ”๊ฐ€ํ•ด๋„ ์‹œ๊ฐ„๋ณต์žก๋„๊ฐ€ ์—„์ฒญ๋‚˜๊ฒŒ ์ข‹์•„์งˆ๊ฒƒ ๊ฐ™๋„ค์š” ( O(N) )!

@Yiseull Yiseull self-requested a review June 29, 2026 10:46
- memo ๋ฅผ ์ด์šฉํ•œ ์‹œ๊ฐ„ ๋ณต์žก๋„ ๋‹จ์ถ•

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์˜ค ์ด์ œ ์ ์ ˆํ•œ ์‹œ๊ฐ„๋ณต์žก๋„๋„ค์š”!
์ •๋‹ต์ด ํ”ผ๋ณด๋‚˜์น˜ ์ˆ˜์—ด์ธ๊ฒƒ๊นŒ์ง€ ์•„์‹ ๋‹ค๋ฉด ๊ณต๊ฐ„๋ณต์žก๋„๋„ ํ›จ์”ฌ ์ค„์ด์‹ค์ˆ˜ ์žˆ์œผ์‹ค๊ฒƒ ๊ฐ™์•„์š”!
๊ณ ์ƒํ•˜์…จ์Šต๋‹ˆ๋‹ค.

Comment thread 3sum/essaysir.java

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๐Ÿท๏ธ ์•Œ๊ณ ๋ฆฌ์ฆ˜ ํŒจํ„ด ๋ถ„์„

  • ํŒจํ„ด: Brute Force, Hash Map / Hash Set
  • ์„ค๋ช…: ์„ธ ๊ฐ€์ง€ ์ˆ˜์˜ ๋ชจ๋“  ์กฐํ•ฉ์„ ๋‚˜์—ดํ•˜๊ณ  ํ•ฉ์ด 0์ธ ๊ฒฝ์šฐ๋ฅผ ๊ฑธ๋Ÿฌ๋‚ด๋Š” ๋ฐฉ์‹์œผ๋กœ, ๋ฌธ์ œ์˜ ํ•ด๋ฅผ ๋ชจ๋‘ ํƒ์ƒ‰ํ•˜๋Š” brute-force ํŒจํ„ด์— ๋”ํ•ด ์ค‘๋ณต ์ œ๊ฑฐ๋ฅผ ์œ„ํ•ด Hash Set์„ ํ™œ์šฉํ•ฉ๋‹ˆ๋‹ค.

๐Ÿ“Š ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„ ๋ถ„์„

๋ณต์žก๋„
Time O(n^3)
Space O(n^2)

ํ”ผ๋“œ๋ฐฑ: ์ „์ฒด ๊ฐ€๋Šฅํ•œ 3์ค‘ ๋ฃจํ”„๋ฅผ ํ†ตํ•ด ๊ฒฝ์šฐ๋ฅผ ๋ชจ๋‘ ๋‚˜์—ดํ•œ ๋’ค ํ•ฉ์ด 0์ธ ๊ฒฝ์šฐ๋ฅผ Set์— ์ €์žฅํ•˜๋ฏ€๋กœ ๋น„ํšจ์œจ์ ์ด๋‹ค. ์ค‘๋ณต ์ œ๊ฑฐ๋Š” LinkedHashSet์œผ๋กœ ์ˆ˜ํ–‰๋˜๋‚˜ ์‹œ๊ฐ„์€ ๊ธ‰๊ฒฉํžˆ ์ฆ๊ฐ€ํ•œ๋‹ค.

๊ฐœ์„  ์ œ์•ˆ: ๊ณ ๋ คํ•ด๋ณผ ๋งŒํ•œ ๋Œ€์•ˆ: ํˆฌ ํฌ์ธํ„ฐ๋ฅผ ์ด์šฉํ•œ ์ •๋ ฌ ํ›„ O(n^2) ์•Œ๊ณ ๋ฆฌ์ฆ˜์œผ๋กœ ๊ตฌํ˜„ํ•˜์—ฌ ์‹œ๊ฐ„ ๋ณต์žก๋„๋ฅผ ํฌ๊ฒŒ ๋‚ฎ์ถœ ์ˆ˜ ์žˆ๋‹ค.

๐Ÿ’ก ํ’€์ด์— ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„๋ฅผ ์ฃผ์„์œผ๋กœ ๋‚จ๊ฒจ๋ณด์„ธ์š”!

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๐Ÿท๏ธ ์•Œ๊ณ ๋ฆฌ์ฆ˜ ํŒจํ„ด ๋ถ„์„

  • ํŒจํ„ด: Dynamic Programming, Hash Map / Hash Set
  • ์„ค๋ช…: ์ฝ”๋“œ๊ฐ€ ์žฌ๊ท€๋กœ ํ”ผ๋ณด๋‚˜์น˜ ํ˜•ํƒœ์˜ ์ค‘๋ณต ๋ถ€๋ถ„ ๋ฌธ์ œ๋ฅผ ํ•ด๊ฒฐํ•˜๋ฉฐ, memoization์œผ๋กœ ๊ฒฐ๊ณผ๋ฅผ ์ €์žฅํ•ด ๋‹ค์ด๋‚˜๋ฏน ํ”„๋กœ๊ทธ๋ž˜๋ฐ ํŒจํ„ด์„ ์‚ฌ์šฉํ•ฉ๋‹ˆ๋‹ค. ํ•ด์‹œ๋งต์„ ์ด์šฉํ•ด ์ด๋ฏธ ๊ณ„์‚ฐํ•œ ๊ฐ’์„ cachingํ•ฉ๋‹ˆ๋‹ค.

๐Ÿ“Š ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„ ๋ถ„์„

๋ณต์žก๋„
Time O(n)
Space O(n)

ํ”ผ๋“œ๋ฐฑ: ๋ฉ”๋ชจํ™”๋ฅผ ํ†ตํ•ด ์ค‘๋ณต ๊ณ„์‚ฐ์„ ์ œ๊ฑฐํ–ˆ์ง€๋งŒ ์žฌ๊ท€ ํ˜ธ์ถœ๋กœ ๊นŠ์ด๊ฐ€ ์ปค์ง€๋ฉด ์Šคํƒ์˜ค๋ฒ„ํ”Œ๋กœ๊ฐ€ ๋ฐœ์ƒํ•  ์ˆ˜ ์žˆ๋‹ค.

๊ฐœ์„  ์ œ์•ˆ: ํ˜„์žฌ ๊ตฌํ˜„์ด ์ ์ ˆํ•ด ๋ณด์ž…๋‹ˆ๋‹ค.

๐Ÿ’ก ํ’€์ด์— ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„๋ฅผ ์ฃผ์„์œผ๋กœ ๋‚จ๊ฒจ๋ณด์„ธ์š”!

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๐Ÿท๏ธ ์•Œ๊ณ ๋ฆฌ์ฆ˜ ํŒจํ„ด ๋ถ„์„

  • ํŒจํ„ด: Greedy, Division
  • ์„ค๋ช…: ๋ฐฐ์—ด ์›์†Œ์˜ ๊ณฑ์„ ๊ฐ ์œ„์น˜์—์„œ ๋‚˜๋ˆ„์–ด ๊ตฌํ•˜๋Š” ๋ฐฉ์‹์€ ๋ถ„ํ•  ์—†์ด ์ „์ฒด ๊ณฑ์„ ํ•œ ๋ฒˆ ๊ณ„์‚ฐํ•œ ๋’ค ๊ฐ ์›์†Œ๋กœ ๋‚˜๋ˆ„๋Š” ์•„์ด๋””์–ด๋กœ, ํƒ์ƒ‰์ด๋‚˜ ์ตœ์ ํ™”๋ณด๋‹ค๋Š” ๊ฐ’์˜ ์กฐํ•ฉ ๊ทœ์น™์— ์˜์กดํ•˜๋Š” ํŒจํ„ด์ž…๋‹ˆ๋‹ค. ๋˜ํ•œ 0 ์ฒ˜๋ฆฌ ๋กœ์ง์ด ์กฐ๊ฑด ๋ถ„๊ธฐ๋กœ ๊ตฌ์„ฑ๋˜์–ด ์žˆ์–ด ๊ฐ„์ ‘์ ์œผ๋กœ Greedy ์„ฑ๊ฒฉ์˜ ์„ ํƒ์  ํŒ๋‹จ์ด ํฌํ•จ๋ฉ๋‹ˆ๋‹ค.

๐Ÿ“Š ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„ ๋ถ„์„

๋ณต์žก๋„
Time O(n)
Space O(1)

ํ”ผ๋“œ๋ฐฑ: 0์˜ ๊ฐœ์ˆ˜์— ๋”ฐ๋ฅธ ๋ถ„๊ธฐ ์ฒ˜๋ฆฌ๋กœ 0์ด ๋‹ค์ˆ˜ ์žˆ์„ ๋•Œ๋„ ์˜ฌ๋ฐ”๋ฅด๊ฒŒ ๋™์ž‘ํ•œ๋‹ค.

๊ฐœ์„  ์ œ์•ˆ: 0 ์ œ๊ฑฐ ์—†์ด ์ขŒ์šฐ ๋ˆ„์  ๊ณฑ์„ ๋‘ ๋ฐฐ์—ด๋กœ ๊ตฌํ•ด๋„ ๋™์ผํ•œ ์‹œ๊ฐ„๋ณต์žก๋„๋ฅผ ๊ฐ€์ง€๋‚˜, ์ถœ๋ ฅ ๊ณต๊ฐ„์€ ๋™์ผํ•˜๊ฒŒ ์œ ์ง€๋œ๋‹ค.

๐Ÿ’ก ํ’€์ด์— ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„๋ฅผ ์ฃผ์„์œผ๋กœ ๋‚จ๊ฒจ๋ณด์„ธ์š”!

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๐Ÿท๏ธ ์•Œ๊ณ ๋ฆฌ์ฆ˜ ํŒจํ„ด ๋ถ„์„

  • ํŒจํ„ด: Hash Map / Hash Set
  • ์„ค๋ช…: ๋‘ ๋ฌธ์ž์—ด์˜ ๋ฌธ์ž ๋นˆ๋„์ˆ˜๋ฅผ ํ•ด์‹œ ๋งต์œผ๋กœ ๋น„๊ตํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ ์•„๋‚˜๊ทธ๋žจ ์—ฌ๋ถ€๋ฅผ ํŒ๋‹จํ•œ๋‹ค. ๊ฐ ๋ฌธ์ž ๋“ฑ์žฅ ํšŸ์ˆ˜๋ฅผ ๋งต์— ๋ˆ„์ ํ•˜๊ณ  ์ตœ์ข…์ ์œผ๋กœ ๋‘ ๋งต์˜ ๋™์ผ์„ฑ์œผ๋กœ ๊ฒฐ๊ณผ๋ฅผ ๋„์ถœํ•œ๋‹ค.

๐Ÿ“Š ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„ ๋ถ„์„

๋ณต์žก๋„
Time O(n + m)
Space O(k)

ํ”ผ๋“œ๋ฐฑ: ๋‘ ๋งต์„ ๋น„๊ตํ•˜๋Š” ๋‹จ์ˆœ ๊ตฌํ˜„์œผ๋กœ ์ง๊ด€์ ์ด์ง€๋งŒ, ๋ฐฐ์—ด ์ฐจ์›์œผ๋กœ ์ตœ์ ํ™” ๊ฐ€๋Šฅํ•˜๋‹ค.

๊ฐœ์„  ์ œ์•ˆ: ํ˜„์žฌ ๊ตฌํ˜„์ด ์ ์ ˆํ•ด ๋ณด์ž…๋‹ˆ๋‹ค.

๐Ÿ’ก ํ’€์ด์— ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„๋ฅผ ์ฃผ์„์œผ๋กœ ๋‚จ๊ฒจ๋ณด์„ธ์š”!

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๐Ÿท๏ธ ์•Œ๊ณ ๋ฆฌ์ฆ˜ ํŒจํ„ด ๋ถ„์„

  • ํŒจํ„ด: Binary Search, Divide and Conquer
  • ์„ค๋ช…: BST ์œ ํšจ์„ฑ ๊ฒ€์‚ฌ๋ฅผ ์žฌ๊ท€์ ์œผ๋กœ ์ˆ˜ํ–‰ํ•˜๋ฉฐ, ๊ฐ ๋…ธ๋“œ์— ๋Œ€ํ•ด ํ—ˆ์šฉ ๋ฒ”์œ„๋ฅผ ์ขํ˜€๊ฐ€๋ฉฐ(left<๊ฐ’<right) ์˜ฌ๋ฐ”๋ฅธ ์ด์ง„ ํƒ์ƒ‰ ํŠธ๋ฆฌ์ธ์ง€ ํ™•์ธํ•œ๋‹ค. ๋ถ„ํ• ํ•˜์—ฌ ๋ฌธ์ œ๋ฅผ ๋ถ€๋ถ„ ๋ฌธ์ œ๋กœ ํ•ด๊ฒฐํ•˜๋Š” ๋ฐฉ์‹์œผ๋กœ ๊ตฌํ˜„๋œ ํŒจํ„ด์ด๋‹ค.

๐Ÿ“Š ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„ ๋ถ„์„

๋ณต์žก๋„
Time O(n)
Space O(h)

ํ”ผ๋“œ๋ฐฑ: ์ „ํ˜•์ ์ธ ์ตœ์†Œ-์™€ ์ตœ๋Œ€ ๋ฒ”์œ„ ๊ฒ€์‚ฌ๋ฅผ ํ†ตํ•ด ๋ฌธ์ œ๋ฅผ ํ•ด๊ฒฐํ•œ๋‹ค. ์Œ์ˆ˜/์–‘์ˆ˜ ๊ฒฝ๊ณ„๋„ ์•ˆ์ „ํ•˜๊ฒŒ ์ฒ˜๋ฆฌํ•œ๋‹ค.

๊ฐœ์„  ์ œ์•ˆ: ํ˜„์žฌ ๊ตฌํ˜„์ด ์ ์ ˆํ•ด ๋ณด์ž…๋‹ˆ๋‹ค.

๐Ÿ’ก ํ’€์ด์— ์‹œ๊ฐ„/๊ณต๊ฐ„ ๋ณต์žก๋„๋ฅผ ์ฃผ์„์œผ๋กœ ๋‚จ๊ฒจ๋ณด์„ธ์š”!

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