6. Binary Tree Right Side View

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
 
 class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> result=new ArrayList<>();
        
        if(root==null){
            return result;
        }
        
        Queue<TreeNode> q=new LinkedList<>();
        q.add(root);
        
        while(q.size()>0){
            int count=q.size();
            
            while(count-->0){
                TreeNode val=q.remove();
                if(count==0){
                    result.add(val.val);
                }
                if(val.left!=null){
                    q.add(val.left);
                }
                if(val.right!=null){
                    q.add(val.right);
                }
                
            }
        }
        return result;            
    }
}
 
class Solution {
    
    List<Integer> result=new ArrayList<>();
    public List<Integer> rightSideView(TreeNode root) {
        
        levelOrder(root,0);
        return result;
    }
    
    void levelOrder(TreeNode node,int level){
        if(node==null){
            return;
        }
        
        if(result.size()==level){
            result.add(node.val);
        }
        
        levelOrder(node.right,level+1);
        levelOrder(node.left,level+1);
    }
}