1 题目

给定一个二叉树，返回该二叉树由底层到顶层的层序遍历，（从左向右，从叶子节点到根节点，一层一层的遍历）

2 解法

2.1 我的最初解法

按照正常的层序遍历应该是从上到下的,只要用一个栈先临时存一下每一层的,在循环一遍:

/** * struct TreeNode { * int val; * struct TreeNode *left; * struct TreeNode *right; * }; */ class Solution { public: /** * * @param root TreeNode类 * @return int整型vector<vector<>> */ vector<vector<int> > levelOrderBottom(TreeNode* root) { // write code here vector<vector<int>> res; if (root) { stack<vector<int>> tS; queue<TreeNode*> tQ; tQ.push(root); while (!tQ.empty()) { int queueSize = tQ.size(); vector<int> tV; for (int i = 0; i < queueSize; i ++) { TreeNode* tmpNode = tQ.front(); tQ.pop(); tV.push_back(tmpNode->val); if (tmpNode->left) tQ.push(tmpNode->left); if (tmpNode->right) tQ.push(tmpNode->right); } tS.push(tV); } while (!tS.empty()) { vector<int> tV = tS.top(); tS.pop(); res.push_back(tV); } } return res; } };