简单的二分查找法

二分查找法

def search(num,l,start=None,end=None):
    start = start if start else 0
    end = end if end is not None else len(l) - 1
    mid = (end - start)//2 + start
    if start > end:
        return None
    elif l[mid] > num :
        return search(num,l,start,mid-1)
    elif l[mid] < num:
        return search(num,l,mid+1,end)
    elif l[mid] == num:
        return mid