void traverse(node){

  if(node.left!=null) traverse(node.left);

  if(node.right!=null) traverse(node.right);

  //do something, current node is the deep leaf(left or right)

}

int traverse(node){

  if(node.left!=null) l = traverse(node.left); // value is its left child

  if(node.right!=null) r = traverse(node.right); // value of its right child

  //do something, current node is the deep leaf(left or right)

  return node.val;

}

/**

 * Definition for a binary tree node.

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

class Solution {

    public TreeNode pruneTree(TreeNode root) {

        int val = traverse(root);

        if(val == 0 && root.left==null && root.right==null) root=null;

        return root;

    }

    int traverse(TreeNode node){//when for

        //lright root

        int tag = 0;

        if(node.left!=null){

            int l = traverse(node.left);//retur the vale of next layer(left child)

            if(l==0) {

                node.left = null;

                tag ++;

            } 

        }else tag++;

        if(node.right!= null){

            int r = traverse(node.right);

            if(r== 0) {

                node.right = null;

                tag ++;

            }

        }else tag ++;

        //root

        if(node.val==0 && tag==2)//remove this node

            return 0;

        else return 1;

    }

}