在有序列表中查找指定值
 1 def find(array,key):
 2     if not array:
 3         raise
 4     low, high = 0, len(array)
 5     while low<=high:
 6         avg = (low+high)/2
 7         if key==array[avg]:
 8             return avg
 9         elif key>array[avg]:
10             low = avg+1
11         else:
12             high = avg-1
13     return -1