点击打开链接
class Solution { public: vector<vector<int>> levelOrderBottom(TreeNode* root) { vector<vector<int>> res; queue<TreeNode*> Q; if(root) Q.push(root); stack<vector<int>> st; while (!Q.empty()) { int count = 0; int levCount = Q.size(); vector<int> levNode; while (count < levCount) { TreeNode* curNode = Q.front(); Q.pop(); levNode.push_back(curNode->val); if(curNode->left) Q.push(curNode->left); if(curNode->right) Q.push(curNode->right); count+=1; } st.push(levNode); } while (!st.empty()) { res.push_back(st.top()); st.pop(); } return res; } };