diff --git a/kata/7-kyu/count-the-ones/README.md b/kata/7-kyu/count-the-ones/README.md
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+# [Count the Ones](https://www.codewars.com/kata/count-the-ones "https://www.codewars.com/kata/5519e930cd82ff8a9a000216")
+
+The __Hamming weight__ of a string is the number of symbols that are different from the zero-symbol of the alphabet used. There are several
+algorithms for efficient computing of the Hamming weight for numbers. In this Kata, speaking technically, you have to find out the number
+of '1' bits in a binary representation of a number. Thus,
+
+```
+hammingWeight(10) // 1010 => 2
+hammingWeight(21) // 10101 => 3
+```
+
+The interesting part of this task is that you have to do it *without* string operation (hey, it's not really interesting otherwise)
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diff --git a/kata/7-kyu/count-the-ones/main/HammingWeight.java b/kata/7-kyu/count-the-ones/main/HammingWeight.java
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+++ b/kata/7-kyu/count-the-ones/main/HammingWeight.java
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+interface HammingWeight {
+  static int hammingWeight(int i) {
+    return Integer.bitCount(i);
+  }
+}
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diff --git a/kata/7-kyu/count-the-ones/test/SolutionTest.java b/kata/7-kyu/count-the-ones/test/SolutionTest.java
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+++ b/kata/7-kyu/count-the-ones/test/SolutionTest.java
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+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+class SolutionTest {
+  @ParameterizedTest
+  @CsvSource(textBlock = """
+      10, 2
+      21, 3
+      """)
+  void sample(int n, int expected) {
+    assertEquals(expected, HammingWeight.hammingWeight(n));
+  }
+}
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diff --git a/kata/7-kyu/index.md b/kata/7-kyu/index.md
index 2f559797..e50a6af5 100644
--- a/kata/7-kyu/index.md
+++ b/kata/7-kyu/index.md
@@ -119,6 +119,7 @@
 - [Count consonants](count-consonants "564e7fc20f0b53eb02000106")
 - [Count the Digit](count-the-digit "566fc12495810954b1000030")
 - [Count the divisors of a number](count-the-divisors-of-a-number "542c0f198e077084c0000c2e")
+- [Count the Ones](count-the-ones "5519e930cd82ff8a9a000216")
 - [Covfefe](covfefe "592fd8f752ee71ac7e00008a")
 - [Create palindrome](create-palindrome "5b7bd90ef643c4df7400015d")
 - [Credit card issuer checking](credit-card-issuer-checking "5701e43f86306a615c001868")