leetcode 144 Binary Tree Preorder Traversal C++

前序遍历。一次AC。

    vector<int> preorderTraversal(TreeNode* root) {
        stack<TreeNode*> stack;
        vector<int> result;
        if (!root) return result;
        stack.push(root);
        while(!stack.empty()) {
            TreeNode *node = stack.top();
            stack.pop();
            result.push_back(node->val);
            if(node->right) stack.push(node->right);
            if(node->left) stack.push(node->left);
        }
        return result;
    }