add folders for week 5

Author: DaleSeo

3sum/README.md

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+- 문제: https://leetcode.com/problems/3sum/
+- 풀이: https://www.algodale.com/problems/3sum/

encode-and-decode-strings/README.md

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+- 문제
+	- 유료: https://leetcode.com/problems/encode-and-decode-strings/
+	- 무료: https://www.lintcode.com/problem/659/
+- 풀이: https://www.algodale.com/problems/encode-and-decode-strings/

longest-consecutive-sequence/README.md

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+- 문제: https://leetcode.com/problems/longest-consecutive-sequence/
+- 풀이: https://www.algodale.com/problems/longest-consecutive-sequence/

product-of-array-except-self/README.md

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+- 문제: https://leetcode.com/problems/product-of-array-except-self/
+- 풀이: https://www.algodale.com/problems/product-of-array-except-self/

top-k-frequent-elements/README.md

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+- 문제: https://leetcode.com/problems/top-k-frequent-elements/
+- 풀이: https://www.algodale.com/problems/top-k-frequent-elements/