39.II 199. 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 {
    List<Integer> ans = new ArrayList<Integer>();
    public List<Integer> rightSideView(TreeNode root) {
        dfs(root,0);//level is 0
        return ans;
        
    }

    private void dfs(TreeNode root,int level){
        if(root==null){
            return;
        }

        if(level==ans.size()){
            ans.add(root.val);
        }

        dfs(root.right,level+1);
        dfs(root.left,level+1);
    }
}