minimum

 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class  {
    public int run(TreeNode root) {
       if(root==null)
           return 0;
       int left=run(root.left);
       int right=run(root.right);
       if(left==0) return right+1;
       if(right==0) return left+1;
       return Math.min(left,right)+1;
    }
}