cs: add “1448. Count Good Nodes in Binary Tree”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/count-good-nodes-in-binary-tree.cs

@@ -0,0 +1,25 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public int val;
+ *     public TreeNode left;
+ *     public TreeNode right;
+ *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+public class Solution {
+    private int GoodNodes(TreeNode root, int m) {
+        if (root == null) {
+            return 0;
+        }
+
+        int newMax = Math.Max(m, root.val);
+        return (root.val >= m ? 1 : 0) + GoodNodes(root.left, newMax) + GoodNodes(root.right, newMax);
+    }
+
+    public int GoodNodes(TreeNode root) => GoodNodes(root, int.MinValue);
+}