5种 ....0...0....0......0.........0.. .../.../......\......\......./.\. ..0...0........0......0.....0...0 ./.....\....../........\......... 0.......0....0..........0........ 二叉树,顾名思义,其一个节点下面允许有两个分支,或左或右,已知三个节点,如上图的0,就一共有五种情况,自己画一下就知道