Add C++ solution of problem #145

Author: Cuda-Chen

145/solution.cpp

@@ -0,0 +1,29 @@
+/**
+ * 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:
+    vector<int> postorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        f(root, ans);
+        return ans;
+    }
+
+private:
+    void f(TreeNode *root, vector<int> &ans) {
+        if(!root)
+            return;
+
+        f(root->left, ans);
+        f(root->right, ans);
+        ans.push_back(root->val);
+    }
+};