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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]]
只是在上篇的基础上，使用了栈结构来存放值，然后复制到vector<vector<int>>中。
C++代码实现：
#include<iostream>#include<new>#include<vector>#include<stack>using namespace std;//Definition for binary treestruct TreeNode{ int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {}};class Solution{public: vector<vector<int> > levelOrderBottom(TreeNode *root) { stack<vector<int> > st; vector<vector<int> > vec; vector<vector<TreeNode*> > rvec; size_t i=0; if(root==NULL) return vector<vector<int> >(); st.push({root->val}); rvec.push_back({root}); vector<int> v1; vector<TreeNode*> v2; while(st.size()&&rvec.size()) { v1.clear(); v2.clear(); for(i=0; i<rvec[rvec.size()-1].size(); i++) { TreeNode *tmp=rvec[rvec.size()-1][i]; if(tmp->left) { v1.push_back(tmp->left->val); v2.push_back(tmp->left); } if(tmp->right) { v1.push_back(tmp->right->val); v2.push_back(tmp->right); } } if(!v1.empty()&&!v2.empty()) { st.push(v1); rvec.push_back(v2); } else break; } while(!st.empty()) { vec.push_back(st.top()); st.pop(); } return vec; } void createTree(TreeNode *&root) { int i; cin>>i; if(i!=0) { root=new TreeNode(i); if(root==NULL) return; createTree(root->left); createTree(root->right); } }};int main(){ Solution s; TreeNode *root; s.createTree(root); vector<vector<int> > vec=s.levelOrderBottom(root); for(auto a:vec) { for(auto v:a) cout<<v<<" "; cout<<endl; }}
运行结果：
Binary Tree Level Order Traversal II
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