diff --git a/3sum/README.md b/3sum/README.md
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+- 문제: https://leetcode.com/problems/3sum/
+- 풀이: https://www.algodale.com/problems/3sum/
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diff --git a/encode-and-decode-strings/README.md b/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/
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diff --git a/longest-consecutive-sequence/README.md b/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/
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diff --git a/product-of-array-except-self/README.md b/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/
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diff --git a/top-k-frequent-elements/README.md b/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/
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