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BinaryTreeLevelOrderTraversalI.cpp
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53 lines (50 loc) · 1.24 KB
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/**
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) {}
* };
*/
class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode *root) {
vector<vector<int> > ret;
if (!root) return ret;
vector<int> level;
vector<TreeNode*> buf;
buf.push_back(root);
while (!buf.empty()) {
level.clear();
vector<TreeNode*> temp;
for (int i = 0; i < buf.size(); ++i) {
TreeNode* node = buf[i];
level.push_back(node->val);
if (node->left) temp.push_back(node->left);
if (node->right) temp.push_back(node->right);
}
ret.push_back(level);
buf = temp;
}
std::reverse(ret.begin(), ret.end());
return ret;
}
};