107. 二叉树的层序遍历 II and 102. 二叉树的层序遍历 023（BFS模板题打两道）

一：题目

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二：上码

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:vector<vector<int>> levelOrderBottom(TreeNode* root) {vector<vector<int> > ans;stack<vector<int> >s;queue<TreeNode *> q;if(root != NULL) q.push(root);while(!q.empty()){int size = q.size();vector<int> v;for(int i = 0; i < size; i++){TreeNode* ptr = q.front();q.pop();v.push_back(ptr->val);if(ptr->left != NULL)q.push(ptr->left);if(ptr->right != NULL)q.push(ptr->right);    }s.push(v);v.clear();    }while(!s.empty()){ans.push_back(s.top());s.pop();}return ans;}
};

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三

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二:上码

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:vector<vector<int>> levelOrder(TreeNode* root) {vector<vector<int> >ans;queue<TreeNode*> q;//这里队列里装的类型为指针if(root != NULL){q.push(root);}while(!q.empty()){   int size = q.size();vector<int> v;for(int i = 0; i < size; i++){TreeNode* ptr = q.front();q.pop();//将每一行的值装进容器当中v.push_back(ptr->val);//将结点的子结点装进队列if(ptr->left != NULL)q.push(ptr->left);if(ptr->right != NULL)q.push(ptr->right);}ans.push_back(v);v.clear();}return ans;}
};