added solution for symmetric_tree in C++

C++/symmetric_Tree.cpp

@@ -0,0 +1,22 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    bool solve(TreeNode* left, TreeNode* right){
+        if(!left && !right) return true;
+        if(!left || !right) return false;
+        return (left->val == right->val && solve(left->left, right->right) && solve(left->right, right->left));
+    }
+    bool isSymmetric(TreeNode* root) {
+        return solve(root->left, root->right);
+    }
+};