感觉我这个思路好 先记录上一层有几个节点
/** * 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: vector<vector<int>> levelOrder(TreeNode* root) { vector<vector<int>> res; vector<int> path; queue<TreeNode*> q; if(!root) return res; q.push(root); while(!q.empty()){ int len=q.size(); while(len--){ TreeNode* tem=q.front(); q.pop(); path.push_back(tem->val); if(tem->left!=NULL) q.push(tem->left); if(tem->right!=NULL) q.push(tem->right); } res.push_back(path); path.clear(); } return res; } };