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Leetcode:Binary Tree Level Order Traversal II
Given a binary tree, return the bottom-up level order traversal of its nodes‘ values. (ie, from left to right, level by level from leaf to root).
For example:
Given binary tree {3,9,20,#,#,15,7},
3 / 9 20 / 15 7
return its bottom-up level order traversal as:
[ [15,7], [9,20], [3]]
分析：代码如下：
class Solution {public: vector<vector<int> > levelOrderBottom(TreeNode *root) { vector<vector<int> > result; if(root == NULL) return result; vector<vector<TreeNode *> > levels; vector<TreeNode *> prev(1, root); while(!prev.empty()){ levels.push_back(prev); vector<TreeNode *> cur; for(auto i = prev.begin(); i != prev.end(); i++){ if((*i)->left) cur.push_back((*i)->left); if((*i)->right) cur.push_back((*i)->right); } prev = cur; } for(auto i = levels.rbegin(); i != levels.rend(); i++){ vector<int> tmp; for(auto j = i->begin(); j != i->end(); j++) tmp.push_back((*j)->val); result.push_back(tmp); } return result; }};
Leetcode:Binary Tree Level Order Traversal II
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