103 lines
2.3 KiB
Markdown
103 lines
2.3 KiB
Markdown
---
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id: 5e6dd1278e6ca105cde40ea9
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title: Longest common subsequence
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challengeType: 5
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forumTopicId: 385271
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dashedName: longest-common-subsequence
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---
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# --description--
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The **longest common subsequence** (or [**LCS**](http://en.wikipedia.org/wiki/Longest_common_subsequence_problem)) of groups A and B is the longest group of elements from A and B that are common between the two groups and in the same order in each group. For example, the sequences "1234" and "1224533324" have an LCS of "1234":
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***1234***
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***12***245***3***332***4***
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For a string example, consider the sequences "thisisatest" and "testing123testing". An LCS would be "tsitest":
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***t***hi***si***sa***test***
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***t***e***s***t***i***ng123***test***ing.
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Your code only needs to deal with strings.
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For more information on this problem please see [Wikipedia](https://en.wikipedia.org/wiki/Longest_common_subsequence_problem).
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# --instructions--
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Write a case-sensitive function that returns the LCS of two strings. You don't need to show multiple LCS's.
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# --hints--
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`lcs` should be a function.
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```js
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assert(typeof lcs == 'function');
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```
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`lcs("thisisatest", "testing123testing")` should return a string.
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```js
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assert(typeof lcs('thisisatest', 'testing123testing') == 'string');
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```
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`lcs("thisisatest", "testing123testing")` should return `"tsitest"`.
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```js
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assert.equal(lcs('thisisatest', 'testing123testing'), 'tsitest');
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```
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`lcs("ABCDGH", "AEDFHR")` should return `"ADH"`.
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```js
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assert.equal(lcs('ABCDGH', 'AEDFHR'), 'ADH');
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```
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`lcs("AGGTAB", "GXTXAYB")` should return `"GTAB"`.
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```js
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assert.equal(lcs('AGGTAB', 'GXTXAYB'), 'GTAB');
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```
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`lcs("BDACDB", "BDCB")` should return `"BDCB"`.
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```js
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assert.equal(lcs('BDACDB', 'BDCB'), 'BDCB');
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```
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`lcs("ABAZDC", "BACBAD")` should return `"ABAD"`.
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```js
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assert.equal(lcs('ABAZDC', 'BACBAD'), 'ABAD');
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```
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# --seed--
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## --seed-contents--
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```js
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function lcs(a, b) {
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}
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```
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# --solutions--
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```js
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function lcs(a, b) {
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var aSub = a.substr(0, a.length - 1);
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var bSub = b.substr(0, b.length - 1);
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if (a.length === 0 || b.length === 0) {
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return '';
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} else if (a.charAt(a.length - 1) === b.charAt(b.length - 1)) {
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return lcs(aSub, bSub) + a.charAt(a.length - 1);
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} else {
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var x = lcs(a, bSub);
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var y = lcs(aSub, b);
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return (x.length > y.length) ? x : y;
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}
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}
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```
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