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] ]
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; class Solution { public: std::vector<std::vector<int> > levelOrderBottom(TreeNode *root) { dfs(root,0); std::reverse(res.begin(),res.end()); return res; } private: std::vector<std::vector<int>> res; void dfs(TreeNode *root, int level) { if(root == NULL) return; if(level == res.size()) { res.push_back(std::vector<int>()); } res[level].push_back(root->val); dfs(root->left,level+1); dfs(root->right,level+1); } };
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