Data update

Task/Tree-from-nesting-levels/C-sharp/tree-from-nesting-levels.cs

@@ -0,0 +1,70 @@
+public static class TreeFromNestingLevels
+{
+    public static void Main()
+    {
+        List<int[]> tests = [[], [1,2,4], [3,1,3,1], [1,2,3,1], [3,2,1,3], [3,3,3,1,1,3,3,3]];
+        Console.WriteLine($"{"Input",24} -> {"Nested",-32} -> Round-trip");
+        foreach (var test in tests) {
+            var tree = BuildTree(test);
+            string input = $"[{string.Join(", ", test)}]";
+            string roundTrip = $"[{string.Join(", ", tree.ToList())}]";
+            Console.WriteLine($"{input,24} -> {tree,-32} -> {roundTrip}");
+        }
+    }
+
+    private static Tree BuildTree(int[] levels)
+    {
+        Tree root = new(0);
+        Tree current = root;
+        foreach (int level in levels) {
+            while (current.Level > level) current = current.Parent;
+            current = current.Parent.Add(level);
+        }
+        return root;
+    }
+
+    private class Tree
+    {
+        public int Level { get; }
+        public Tree Parent { get; }
+        private readonly List<Tree> children = [];
+
+        public Tree(int level, Tree? parent = null)
+        {
+            Level = level;
+            Parent = parent ?? this;
+        }
+
+        public Tree Add(int level)
+        {
+            if (Level == level) return this;
+            Tree tree = new(Level + 1, this);
+            children.Add(tree);
+            return tree.Add(level);
+        }
+
+        public override string ToString() => children.Count == 0
+            ? (Level == 0 ? "[]" : $"{Level}")
+            : $"[{string.Join(", ", children.Select(c => c.ToString()))}]";
+
+        public List<int> ToList()
+        {
+            List<int> list = [];
+            ToList(this, list);
+            return list;
+        }
+
+        private static void ToList(Tree tree, List<int> list)
+        {
+            if (tree.children.Count == 0) {
+                if (tree.Level > 0) list.Add(tree.Level);
+            } else {
+                foreach (Tree child in tree.children) {
+                    ToList(child, list);
+                }
+            }
+        }
+
+    }
+
+}