题目描述：
输入一个整数数组，判断该数组是不是某二叉搜索树的后序遍历的结果。如果是返回true，否则返回false。假设输入的数组的任意两个数字互不相同。
解题思路：
要明确两个概念：
1. 二叉搜索树的特点，就是如果有对任何一个非空结点，假如左子树存在，那么左子树的中任意一个结点都比该根结点小，假如右子树存在，那么右子树中的任何一个节点都比该根结点大。
2.二叉树的后序遍历，也就是 左→右→根 的遍历顺序。
然后根据一个具体的实例模拟一下过程：
例如输入数组{5、7、6、9、11、10、8}
因为是后序遍历，所以最后一个数字8一定是整棵树的根结点。所以其他数字为8的子结点，从前往后遍历数组，5，7，6都小于8，所以这三个数字应该组成了8的左子树，同理9、11、10组成了8的右子树。
又如输入数组{7、4、6、5}，5是根结点，从前往后遍历数组，5应该是没有左子树，7、4、6组成了5的右子树，而4 < 5，所以，4不能在5的右子树中，相互矛盾，所以这不能是一个后序遍历序列。
以上这些是判断条件，而下面一步是利用递归来判断整棵树了。
代码如下：
<code class="hljs cs has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> VerifySequenceOfBSTTest { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> boolean <span class="hljs-title" style="box-sizing: border-box;">verifySequenceOfBST</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] sequence, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> start, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> end){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(sequence == <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span> || start < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> || end < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>; } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> root = sequence[end]; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = start; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span>( ; i < end; i++){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(sequence[i] > root){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">break</span>; } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> j = i; j < end; j++){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(sequence[j] < root){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>; } } boolean left = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(i > start){ left = verifySequenceOfBST(sequence, start, i - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); } boolean right = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(i < end - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>){ right = verifySequenceOfBST(sequence, i , end - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> (left && right); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] a = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[]{<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">9</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>}; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] b = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[]{<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>}; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[] c = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>[]{<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">9</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>}; System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(verifySequenceOfBST(a, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, a.length - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)); System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(verifySequenceOfBST(b, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, b.length - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)); System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(verifySequenceOfBST(c, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, c.length - <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>)); }}</code> 0 0
