107. Binary Tree Level Order Traversal II
和 102. Binary Tree Level Order Traversal 完全一样，反着往 result 里加即可。
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<List<Integer>> levelOrderBottom(TreeNode root) {
List<List<Integer>> res = new LinkedList<>();
if (root == null) {
return res;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
List<Integer> cur = new LinkedList<>();
for (int i = 0; i < size; i++) {
TreeNode curNode = queue.poll();
cur.add(curNode.val);
if (curNode.left != null) {
queue.offer(curNode.left);
}
if (curNode.right != null) {
queue.offer(curNode.right);
}
}
res.add(0, cur);
}
return res;
}
}