feat: kata/loop-detector

kata/7-kyu/index.md

@@ -320,6 +320,7 @@
 - [London CityHacker](london-cityhacker "5bce125d3bb2adff0d000245")
 - [Longest vowel chain](longest-vowel-chain "59c5f4e9d751df43cf000035")
 - [Looking for a benefactor](looking-for-a-benefactor "569b5cec755dd3534d00000f")
+- [Loop Detector](loop-detector "68851563123e161332d2a84b")
 - [Lost number in number sequence](lost-number-in-number-sequence "595aa94353e43a8746000120")
 - [Love vs friendship](love-vs-friendship "59706036f6e5d1e22d000016")
 - [lucky number](lucky-number "55afed09237df73343000042")

kata/7-kyu/loop-detector/README.md

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+# [Loop Detector](https://www.codewars.com/kata/loop-detector "https://www.codewars.com/kata/68851563123e161332d2a84b")
+
+In this kata, you'll simulate traversing a one-way pointer chain, similar to a singly linked list. Each element in the input list represents
+the index of the next element to move to.
+
+Your task is to determine whether this chain eventually enters a loop, or whether it terminates by stepping out of bounds.
+
+## Function Signature
+
+* ```arr``` is a list or array of non-negative integers.
+
+* Return ```True``` (or your language's equivalent) if the traversal enters a loop.
+
+* Return ```False``` (or your language's equivalent) if the traversal terminates.
+
+## How Traversal Works
+
+* Begin at index ```0```.
+
+* Read the value at the current index to get the next index.
+
+* Continue stepping through the array.
+
+* If you encounter an index you've already visited, you've found a loop — return ```True``` (or your language's equivalent).
+
+* If a step takes you to an index outside the array, the traversal ends — return ```False``` (or your language's equivalent).
+
+## Examples
+
+```
+Input: 1, 2, 3, 4, 2 ➞ True
+Path: 0 -> 1 -> 2 -> 3 -> 4 -> 2 -> ... (loop detected)
+
+Input: 1, 2, 3, 4, 5 ➞ False
+Path: 0 -> 1 -> 2 -> 3 -> 4 -> 5 -> (out of bounds)
+
+Input: 0 ➞ True
+Path: 0 -> 0 -> 0 -> ... (self-loop)
+
+Input: 3, 2, 1, 6 ➞ False
+Path: 0 -> 3 -> 6 -> (out of bounds)
+
+Input: 1, 0 ➞ True
+Path: 0 -> 1 -> 0 -> 1 -> ... (cycle of two)
+```
+
+## Notes
+
+* The input may be empty. In that case, return ```False``` (or your language's equivalent).
+
+* All elements are guaranteed to be non-negative integers.
+
+* You must detect any kind of loop, whether it be a:
+
+LICENSE build.gradle.kts docs gradle gradle.properties gradlew gradlew.bat kata settings.gradle.kts Self-loop (e.g., ```[0]```)
+
+LICENSE build.gradle.kts docs gradle gradle.properties gradlew gradlew.bat kata settings.gradle.kts Two-node loop (e.g., ```[1, 0]```)
+
+LICENSE build.gradle.kts docs gradle gradle.properties gradlew gradlew.bat kata settings.gradle.kts Larger cycle (e.g., ```[1, 2, 0]```)
+
+* An index is considered out of bounds if it is greater than or equal to ```len(arr)```.

kata/7-kyu/loop-detector/main/Kata.java

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+import static java.util.stream.IntStream.iterate;
+
+interface Kata {
+  static boolean hasLoop(int[] arr) {
+    return iterate(0, i -> arr[i]).limit(arr.length + 1L).allMatch(i -> i < arr.length);
+  }
+}

kata/7-kyu/loop-detector/test/SampleTests.java

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+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class SampleTests {
+  @Test
+  void cyclic() {
+    assertTrue(Kata.hasLoop(new int[]{0}));
+    assertTrue(Kata.hasLoop(new int[]{1, 0}));
+    assertTrue(Kata.hasLoop(new int[]{2, 0, 1, 5}));
+    assertTrue(Kata.hasLoop(new int[]{1, 2, 3, 4, 2}));
+  }
+
+  @Test
+  void acyclic() {
+    assertFalse(Kata.hasLoop(new int[0]));
+    assertFalse(Kata.hasLoop(new int[]{3, 2, 1, 4}));
+    assertFalse(Kata.hasLoop(new int[]{1, 2, 3, 4, 5}));
+  }
+}