Create Binary Tree

Binary Tree

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+/**
+ * Definition for a binary tree node.
+ *===================================
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+class Solution {
+public:
+    void build(TreeNode *root, int level_id, vector<vector<int>> &result) {
+
+        if (root == NULL) { return; }
+        // each vector inside the result vector
+        // contains the nodes in a particular level
+        // the level of this vector is the index of the result vector
+        // IE result[0] = {root->val}
+        // result[1] = {root->left->val, root->right->val}
+        // and so on
+
+        // if the size of the of the level_id
+        // then this is the start of a new level
+        // so we have to push a new empty vector where
+        // we will push the nodes at that level
+        if (result.size() == level_id) {
+            result.push_back(vector<int>());
+        }
+
+        if (root != NULL) {
+            result[level_id].push_back(root->val);
+        }
+
+        build(root->left, level_id + 1, result);
+        build(root->right, level_id + 1, result);
+    }
+
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        vector<vector<int>> result = {};
+        build(root, 0, result);
+        return result;
+    }
+};