逐层打印二叉树

struct BinaryTreeNode {
    int nvalue=0;
    BinaryTreeNode* pleft = nullptr;
    BinaryTreeNode* pright = nullptr;
    BinaryTreeNode* parent = nullptr;
};
准备一个队列，通过不断的入队出队，逐层遍历二叉树的节点
vector<vector<int>> BinaryTreePrint(BinaryTreeNode* node) {
    vector<vector<int>> ans;
    if (node == nullptr) {
        throw exception("Invalid Input");
        return ans;
    }
    queue<BinaryTreeNode*>q;
    q.push(node);

    while (!q.empty()) {
        int low = 0, high = q.size();
        vector<int>v;
        while (low++ < high) {

            BinaryTreeNode* temp = q.front();
            v.push_back(temp->nvalue);
            q.pop();
            if (temp->pleft) {
                q.push(temp->pleft);
            }
            if (temp->pright) {
                q.push(temp->pright);
            }
        }
        ans.push_back(v);
    }
    return ans;
}