b c d e f g q r s t 二分查找,折半法
① low = 0,high = 9,mid = (low+ high)/2=4, ∴ 'b'比较a[4]='f',<,找左边
( b~e )
② low = 0,high = mid-1 = 3, mid = 3/2=1, ∴ 'b'比较a[1]='c'
, <,找左边(b~b)
③ low = 0,high = mid -1 = 0,mid = 0,∴ 'b' 比较a[0] =
'b',找到(若未找到,low=high,也停止查找)
所以比较的顺序就是f c b