236. Lowest Common Ancestor of a Binary Tree via Java

level order traversal solution in Java

public class Solution {
  public List<Integer> rightView(TreeNode root) {
    // Write your solution here
    List<Integer> view = new ArrayList<>();
    if(root==null){
      return view;
    }
    Queue<TreeNode> layer = new LinkedList<>();
    layer.offer(root);
    while(layer.size()>=1){
      int count = layer.size();
      for(int i = 0; i<count; i++){
        TreeNode curNode = layer.poll();
        if(curNode.left!=null){
          layer.offer(curNode.left);
        }
        if(curNode.right!=null){
          layer.offer(curNode.right);
        }
        if(i == count-1){
          view.add(curNode.key);
        }
      }
    }
    return view;
  }
}

time: O(n)  we do O(1) operation to each treeNode

space: O(n) use to keep our result:O(n) queue to store treeNode: O(n)