BFS
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| class Solution {
public List<List<Integer>> levelOrderBottom(TreeNode root) {
List<List<Integer>> resultList = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
if (root != null) {
queue.offer(root);
}
while (!queue.isEmpty()) {
List<Integer> numList = new ArrayList<>(queue.size());
for (int i = queue.size(); i > 0; i--) {
TreeNode node = queue.poll();
numList.add(node.val);
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
resultList.add(numList);
}
Collections.reverse(resultList);
return resultList;
}
}
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BFS
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| class Solution {
public List<List<Integer>> levelOrderBottom(TreeNode root) {
List<List<Integer>> resultList = new ArrayList<>();
Queue<TreeNode> queue = new LinkedList<>();
if (root != null) {
queue.offer(root);
}
while (!queue.isEmpty()) {
List<Integer> numList = new ArrayList<>(queue.size());
for (int i = queue.size(); i > 0; i--) {
TreeNode node = queue.poll();
numList.add(node.val);
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
resultList.add(numList);
}
Collections.reverse(resultList);
return resultList;
}
}
|
References
107. Binary Tree Level Order Traversal II