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] ]
class Solution {
public:
vector<vector<int>> levelOrderBottom(TreeNode* root) {
vector<vector<int>> arr;
if(root==NULL)
return arr;
queue<TreeNode *> q;
q.push(root);
while(!q.empty())
{
int i = 0;
int height = q.size();
vector<int> c;
while(i++<height)
{
TreeNode* t = q.front();
q.pop();
c.push_back(t->val);
if(t->left)
q.push(t->left);
if(t->right)
q.push(t->right);
}
arr.push_back(c);
}
int n = arr.size();
for(int i=0;i<n/2;i++)
{
vector<int> temp = arr[i];
arr[i] = arr[n-1-i];
arr[n-1-i] = temp;
}
return arr;
}
};
