problems: add n-ary tree level-order traversal

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

problems/n-ary-tree-level-order-traversal.cpp

@@ -0,0 +1,47 @@
+/*
+// Definition for a Node.
+class Node {
+public:
+    int val;
+    vector<Node*> children;
+
+    Node() { }
+
+    Node(int _val)
+    {
+        val = _val;
+    }
+
+    Node(int _val, vector<Node*> _children)
+    {
+        val = _val;
+        children = _children;
+    }
+};
+*/
+
+class Solution {
+    void levelOrder(vector<vector<int>>& traversal, Node* root, int level)
+    {
+        if (root == nullptr) {
+            return;
+        }
+
+        if (level >= traversal.size()) {
+            traversal.push_back({});
+        }
+        traversal[level].push_back(root->val);
+
+        for (auto child : root->children) {
+            levelOrder(traversal, child, level + 1);
+        }
+    }
+
+public:
+    vector<vector<int>> levelOrder(Node* root)
+    {
+        vector<vector<int>> result;
+        levelOrder(result, root, 0);
+        return result;
+    }
+};