feat: LC-0438: Find All Anagrams in a String

add java solution for leetcode problem 438 - Find All Anagrams in a String

solutions-java/src/main/java/dsalgo/string/LC0438_FindAllAnagrams.java

@@ -0,0 +1,48 @@
+package dsalgo.string;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class LC0438_FindAllAnagrams {
+  public List<Integer> findAnagrams(String s, String p) {
+    List<Integer> ans = new ArrayList<>();
+    if (s == null || s.length() == 0 || s.length() < p.length()) {
+      return ans;
+    }
+
+    Map<Character, Integer> map = new HashMap<>();
+    for (char c : p.toCharArray()) {
+      map.put(c, map.getOrDefault(c, 0) + 1);
+    }
+
+    // The number of distinct characters
+    int counter = map.size();
+    for (int left = 0, right = 0; right < s.length(); right++) {
+      char cRight = s.charAt(right);
+      if (map.containsKey(cRight)) {
+        map.put(cRight, map.get(cRight) - 1);
+        if (map.get(cRight) == 0) {
+          counter -= 1;
+        }
+      }
+
+      while (counter <= 0) {
+        char cLeft = s.charAt(left);
+        if (map.containsKey(cLeft)) {
+          map.put(cLeft, map.get(cLeft) + 1);
+          if (map.get(cLeft) > 0) {
+            counter += 1;
+          }
+        }
+        if (right - left + 1 == p.length()) {
+          ans.add(left);
+        }
+        left++;
+      }
+    }
+
+    return ans;
+  }
+}