Add solution to 'a lot' of problems

Easy/same-tree/solution.cpp

@@ -0,0 +1,21 @@
+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 isSameTree(TreeNode *p, TreeNode *q) {
+        if (p != nullptr && q != nullptr) {
+            return p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
+        } else if (p == nullptr ^ q == nullptr) {
+            return false;
+        } else {
+            return true;
+        }
+    }
+};