Update README.md

java solution added

Author: rajenderthota

solution/1900-1999/1948.Delete Duplicate Folders in System/README.md

@@ -135,6 +135,75 @@ tags:
 #### Java
 
 ```java
+class Solution {
+    static class TrieNode {
+        Map<String, TrieNode> children = new HashMap<>();
+        String name;
+        boolean isDeleted = false;
+
+        TrieNode(String name) {
+            this.name = name;
+        }
+    }
+
+    Map<String, List<TrieNode>> serialMap = new HashMap<>();
+
+    public List<List<String>> deleteDuplicateFolder(List<List<String>> paths) {
+        TrieNode root = new TrieNode("");
+        
+        // Step 1: Build the folder trie
+        for (List<String> path : paths) {
+            TrieNode curr = root;
+            for (String folder : path) {
+                curr.children.putIfAbsent(folder, new TrieNode(folder));
+                curr = curr.children.get(folder);
+            }
+        }
+
+        // Step 2: Serialize and collect duplicates
+        serialize(root);
+
+        // Step 3: Mark duplicate folders
+        for (List<TrieNode> group : serialMap.values()) {
+            if (group.size() > 1) {
+                for (TrieNode node : group) {
+                    node.isDeleted = true;
+                }
+            }
+        }
+
+        // Step 4: Collect remaining paths
+        List<List<String>> result = new ArrayList<>();
+        dfs(root, new ArrayList<>(), result);
+        return result;
+    }
+
+    private String serialize(TrieNode node) {
+        if (node.children.isEmpty()) return "";
+
+        List<String> parts = new ArrayList<>();
+        for (String childName : node.children.keySet().stream().sorted().toList()) {
+            TrieNode child = node.children.get(childName);
+            String sub = serialize(child);
+            parts.add(childName + "[" + sub + "]");
+        }
+
+        String serial = String.join("", parts);
+        serialMap.computeIfAbsent(serial, k -> new ArrayList<>()).add(node);
+        return serial;
+    }
+
+    private void dfs(TrieNode node, List<String> path, List<List<String>> result) {
+        for (TrieNode child : node.children.values()) {
+            if (!child.isDeleted) {
+                path.add(child.name);
+                result.add(new ArrayList<>(path));
+                dfs(child, path, result);
+                path.remove(path.size() - 1);
+            }
+        }
+    }
+}
 
 ```