feat:add Solution.cpp for 0102.Binary Tree Level Order Traversal

Author: Stackingrule

solution/0100-0199/0102.Binary Tree Level Order Traversal/Solution.cpp

@@ -0,0 +1,19 @@
+class Solution {
+public:
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        if (!root) return {};
+        vector<vector<int>> res;
+        queue<TreeNode*> q{{root}};
+        while (!q.empty()) {
+            vector<int> oneLevel;
+            for (int i = q.size(); i > 0; --i) {
+                TreeNode* t = q.front(); q.pop();
+                oneLevel.push_back(t->val);
+                if (t->left) q.push(t->left);
+                if (t->right) q.push(t->right);
+            }
+            res.push_back(oneLevel);
+        }        
+        return res;
+    }
+};