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[LeetCode]107 Binary Tree Level Order Traversal II
https://oj.leetcode.com/problems/binary-tree-level-order-traversal-ii/
http://blog.csdn.net/linhuanmars/article/details/23414711
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<List<Integer>> levelOrderBottom(TreeNode root) {
// BFS
if (root == null)
return Collections.<List<Integer>> emptyList();
List<List<Integer>> toReturn = new ArrayList<>();
Queue<TreeNodeWithLevel> queue = new LinkedList<TreeNodeWithLevel>();
queue.offer(new TreeNodeWithLevel(root, 1));
while (!queue.isEmpty())
{
TreeNodeWithLevel n = queue.poll();
if (toReturn.size() < n.level)
{
toReturn.add(0, new ArrayList<Integer>());
}
toReturn.get(toReturn.size() - n.level).add(n.node.val);
if (n.node.left != null)
{
queue.offer(new TreeNodeWithLevel(n.node.left, n.level + 1));
}
if (n.node.right != null)
{
queue.offer(new TreeNodeWithLevel(n.node.right, n.level + 1));
}
}
return toReturn;
}
private static class TreeNodeWithLevel
{
int level;
TreeNode node;
TreeNodeWithLevel(TreeNode node, int level)
{
this.node = node;
this.level = level;
}
}
}[LeetCode]107 Binary Tree Level Order Traversal II
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