tree

代码说明：

  判断二叉树是否是完全二叉树，求二叉树宽度1：若无左子女则不应该有右子女2.求二叉树宽度3.二叉树k层叶子结点(Determine whether the binary tree is a complete binary tree, binary tree width 1: children should not be left if no children have the right width 3. 2. binary tree binary tree leaf node k layer)