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107.BinaryTreeLevelOrderTraversalII(easy).cpp
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107.BinaryTreeLevelOrderTraversalII(easy).cpp
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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,null,null,15,7],
3
/ \
9 20
/ \
15 7
return its bottom-up level order traversal as:
[
[15,7],
[9,20],
[3]
]
*/
/**
* Definition for a binary tree node.
* 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>> v;
if (root == NULL) return v;
queue<TreeNode*> treeQue;
queue<int> levQue;
int lastLev = 1;
vector<int> v_tmp;
treeQue.push(root);
levQue.push(1);
while (treeQue.size() > 0)
{
TreeNode* cur_node = treeQue.front();
treeQue.pop();
int cur_lev = levQue.front();
levQue.pop();
if (cur_lev != lastLev)
{
v.push_back(v_tmp);
v_tmp.clear();
lastLev = cur_lev;
}
v_tmp.push_back(cur_node->val);
if (cur_node->left != NULL)
{
treeQue.push(cur_node->left);
levQue.push(cur_lev+1);
}
if (cur_node->right != NULL)
{
treeQue.push(cur_node->right);
levQue.push(cur_lev+1);
}
}
if (v_tmp.size() > 0)
v.push_back(v_tmp);
reverse(v.begin(), v.end());
return v;
}
};