添加 （0102.二叉树的层序遍历.md）：102.二叉树的层序遍历 增加 c++ 递归版本

problems/0102.二叉树的层序遍历.md

@@ -82,6 +82,26 @@ public:
     }
 };
 ```
+```CPP
+# 递归法
+class Solution {
+public:
+    void order(TreeNode* cur, vector<vector<int>>& result, int depth)
+    {
+        if (cur == nullptr) return;
+        if (result.size() == depth) result.push_back(vector<int>());
+        result[depth].push_back(cur->val);
+        order(cur->left, result, depth + 1);
+        order(cur->right, result, depth + 1);
+    }
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        vector<vector<int>> result;
+        int depth = 0;
+        order(root, result, depth);
+        return result;
+    }
+};
+```
 
 python3代码：