用递归实现的二分法，数据结构的典型问题，二分查找也称折半查找，它要求待查找的数据元素必须是按关键字大小有序排列的顺序表。-Realize the dichotomy with recursive data structure of a typical problem, binary search, also known as split-half search, which requires the data elements to be search by keyword must be orderly arranged in the order of the size of table.