cs: add «1233. Remove Sub-Folders from the Filesystem»

URL:	https://leetcode.com/problems/remove-sub-folders-from-the-filesystem/
Signed-off-by: Matej Focko <me@mfocko.xyz>

cs/remove-sub-folders-from-the-filesystem.cs

@@ -0,0 +1,56 @@
+public class Solution {
+    private class Trie<T> {
+        public class TrieNode {
+            public bool Has;
+            public Dictionary<T, TrieNode> Successors;
+
+            public TrieNode() {
+                Has = false;
+                Successors = new Dictionary<T, TrieNode>();
+            }
+        }
+
+        public TrieNode Root = new TrieNode();
+
+        public void Add(IEnumerable<T> path) {
+            var node = Root;
+            foreach (var element in path) {
+                if (!node.Successors.ContainsKey(element)) {
+                    node.Successors[element] = new TrieNode();
+                }
+                node = node.Successors[element];
+            }
+            node.Has = true;
+        }
+    }
+
+    private void Reconstruct(
+        List<string> result, List<string> path, Trie<string>.TrieNode node
+    ) {
+        if (node == null) {
+            return;
+        }
+
+        if (node.Has) {
+            result.Add(String.Join("/", path));
+            return;
+        }
+
+        foreach (var subdirectory in node.Successors) {
+            path.Add(subdirectory.Key);
+            Reconstruct(result, path, subdirectory.Value);
+            path.RemoveAt(path.Count - 1);
+        }
+    }
+
+    public IList<string> RemoveSubfolders(string[] folder) {
+        var trie = new Trie<string>();
+        foreach (var entry in folder) {
+            trie.Add(entry.Split("/"));
+        }
+
+        var result = new List<string>();
+        Reconstruct(result, new List<string>(), trie.Root);
+        return result;
+    }
+}