二分查找又称折半查找，优点是比较次数少，查找速度快，平均性能好，占用系统内存较少；其缺点是要求待查表为有序表，且插入删除困难。因此，折半查找方法适用于不经常变动而查找频繁的有序列表。首先，假设表中元素是按升序排列，将表中间位置记录的关键字与查找关键字比较，如果两者相等，则查找成功；否则利用中间位置记录将表分成前、后两个子表，如果中间位置记录的关键字大于查找关键字，则进一步查找前一子表，否则进一步查找后一子表。重复以上过程，直到找到满足条件的记录，使查找成功，或直到子表不存在为止，此时查找不成功。(Two search and binary search, the utility model has the advantages of low frequency, average speed, good performance, the system memory is less; the disadvantage is the requirement for 0.9 ordered list, and insert delete difficult. Therefore, the binary search method for an ordered list to find frequent and often change. First of all, the periodic table is assumed in ascending order, compared with the keyword search keywords will form the middle position of the record, if the two are equal, find success; otherwise the middle position recorded before and after the table is divided into two sub tables, if the middle position recorded in a keyword search keywords, before further lookup sub table otherwise, after a further search of the child table. Repeat the above process until the lookup is successful, or until the subtable does not exist, and the lookup is not successful.)