层序遍历
class Solution { public: vector<vector<int> > Print(TreeNode* pRoot) { vector<vector<int>> res; if (!pRoot) return res; queue<TreeNode*> q; q.push(pRoot); while (!q.empty()) { int n = q.size(); vector<int> tmp; for (int i = 0; i < n; i++) { if (q.front()->left) q.push(q.front()->left); if (q.front()->right) q.push(q.front()->right); tmp.push_back(q.front()->val); q.pop(); } res.push_back(tmp); } return res; } };