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85 lines
1.9 KiB
Markdown
85 lines
1.9 KiB
Markdown
---
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id: 69cfca90e8a0a6d4d6871c54
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title: "Challenge 270: Longest Common Substring"
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challengeType: 29
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dashedName: challenge-270
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---
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# --description--
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Given a string, return the longest substring that appears more than once.
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- The substrings can overlap.
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# --hints--
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`get_longest_substring("abracadabra")` should return `"abra"`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(get_longest_substring("abracadabra"), "abra")`)
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}})
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```
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`get_longest_substring("hello world hello")` should return `"hello"`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(get_longest_substring("hello world hello"), "hello")`)
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}})
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```
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`get_longest_substring("mississippi")` should return `"issi"`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(get_longest_substring("mississippi"), "issi")`)
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}})
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```
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`get_longest_substring("ha ha ha ha ha ha ha")` should return `"ha ha ha ha ha ha"`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(get_longest_substring("ha ha ha ha ha ha ha"), "ha ha ha ha ha ha")`)
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}})
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```
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`get_longest_substring("the quick brown fox jumped over the lazy dog that the quick brown fox jumped over")` should return `"the quick brown fox jumped over"`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(get_longest_substring("the quick brown fox jumped over the lazy dog that the quick brown fox jumped over"), "the quick brown fox jumped over")`)
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}})
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```
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# --seed--
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## --seed-contents--
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```py
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def get_longest_substring(s):
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return s
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```
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# --solutions--
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```py
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def get_longest_substring(s):
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longest = ''
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for length in range(len(s) - 1, 0, -1):
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for i in range(len(s) - length + 1):
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sub = s[i:i + length]
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if s.find(sub) != s.rfind(sub):
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return sub
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return longest
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```
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