Add solution of FindAllAnagramsInAString task

Author: andrei-punko

src/main/java/by/andd3dfx/string/FindAllAnagramsInAString.java

@@ -0,0 +1,56 @@
+package by.andd3dfx.string;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/find-all-anagrams-in-a-string/">Task description</a>
+ *
+ * Given two strings s and p, return an array of all the start indices of p's in s. You may return the answer in any order.
+ *
+ * Example 1:
+ *   Input: s = "cbaebabacd", p = "abc"
+ *   Output: [0,6]
+ *   Explanation:
+ *   The substring with start index = 0 is "cba", which is an anagram of "abc".
+ *   The substring with start index = 6 is "bac", which is an anagram of "abc".
+ *
+ * Example 2:
+ *   Input: s = "abab", p = "ab"
+ *   Output: [0,1,2]
+ *   Explanation:
+ *   The substring with start index = 0 is "ab", which is an anagram of "ab".
+ *   The substring with start index = 1 is "ba", which is an anagram of "ab".
+ *   The substring with start index = 2 is "ab", which is an anagram of "ab".
+ * </pre>
+ */
+public class FindAllAnagramsInAString {
+
+    public static List<Integer> findAnagrams(String s, String p) {
+        List<Integer> result = new ArrayList<>();
+        var normalizedP = normalize(p);
+
+        Set<String> approvedStrings = new HashSet<>();
+        approvedStrings.add(normalizedP);
+        for (var start = 0; start <= s.length() - p.length(); start++) {
+            String candidate = s.substring(start, start + p.length());
+
+            if (approvedStrings.contains(candidate) || normalizedP.equals(normalize(candidate))) {
+                approvedStrings.add(candidate);
+                result.add(start);
+            }
+        }
+
+        return result;
+    }
+
+    private static String normalize(String p) {
+        var chars = p.toCharArray();
+        Arrays.sort(chars);
+        return new String(chars);
+    }
+}

src/test/java/by/andd3dfx/string/FindAllAnagramsInAStringTest.java

@@ -0,0 +1,18 @@
+package by.andd3dfx.string;
+
+import org.junit.Test;
+
+import java.util.List;
+
+import static by.andd3dfx.string.FindAllAnagramsInAString.findAnagrams;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class FindAllAnagramsInAStringTest {
+
+    @Test
+    public void testFindAnagrams() {
+        assertThat(findAnagrams("cbaebabacd", "abc")).isEqualTo(List.of(0, 6));
+        assertThat(findAnagrams("abab", "ab")).isEqualTo(List.of(0, 1, 2));
+        assertThat(findAnagrams("abcabc", "cz")).isEqualTo(List.of());
+    }
+}