Find all anagrams in a string

Author: nikoo28

src/main/java/leetcode/medium/FindAllAnagramsInAString.java

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+package leetcode.medium;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class FindAllAnagramsInAString {
+
+  List<Integer> findAnagrams(String s, String p) {
+
+    int[] pCount = new int[26];
+    int[] sCount = new int[26];
+    List<Integer> result = new java.util.ArrayList<>();
+
+    // Count frequency of characters in p
+    for (char c : p.toCharArray()) {
+      pCount[c - 'a']++;
+    }
+
+    // Sliding window to count frequency of characters in s
+    for (int i = 0; i < s.length(); i++) {
+      sCount[s.charAt(i) - 'a']++;
+
+      // Remove the character that is out of the window
+      if (i >= p.length()) {
+        sCount[s.charAt(i - p.length()) - 'a']--;
+      }
+
+      // Compare counts
+      if (Arrays.equals(pCount, sCount)) {
+        result.add(i - p.length() + 1);
+      }
+    }
+
+    return result;
+  }
+
+}

src/test/java/leetcode/medium/FindAllAnagramsInAStringTest.java

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+package leetcode.medium;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class FindAllAnagramsInAStringTest {
+
+  private final FindAllAnagramsInAString findAllAnagramsInAString;
+
+  FindAllAnagramsInAStringTest() {
+    findAllAnagramsInAString = new FindAllAnagramsInAString();
+  }
+
+  @Test
+  void testFindAnagrams1() {
+    String s = "cbaebabacd";
+    String p = "abc";
+    assertEquals(List.of(0, 6), findAllAnagramsInAString.findAnagrams(s, p));
+  }
+
+  @Test
+  void testFindAnagrams2() {
+    String s = "abab";
+    String p = "ab";
+    assertEquals(List.of(0, 1, 2), findAllAnagramsInAString.findAnagrams(s, p));
+  }
+
+  @Test
+  void testFindAnagrams3() {
+    String s = "aaaaaaaaaa";
+    String p = "a";
+    assertEquals(List.of(0, 1, 2, 3, 4, 5, 6, 7, 8, 9), findAllAnagramsInAString.findAnagrams(s, p));
+  }
+
+  @Test
+  void testFindAnagrams4() {
+    String s = "abababab";
+    String p = "ab";
+    assertEquals(List.of(0, 1, 2, 3, 4, 5, 6), findAllAnagramsInAString.findAnagrams(s, p));
+  }
+}