搜索算法

一、二分法查找

def search(alist,item,start=0,end=0):
    # print("%s-%s" % (start, end))
    if start > end:
        return None

    mid = (start + end) // 2

    if alist[mid] == item:
        return mid
    elif alist[mid] > item:
        return search(alist, item, start, mid - 1)
    else:
        return search(alist, item, mid + 1, end)

def binary_search(alist,item):
    """二分查找"""
    return search(alist,item,0,len(alist) -1)

if __name__ == '__main__':
    a = [1, 2, 3, 4, 5,6, 242, 823]
    ret = binary_search(a, 1)
    print(ret)

    ret = binary_search(a, 2)
    print(ret)

    ret = binary_search(a, 3)
    print(ret)

    ret = binary_search(a, 4)
    print(ret)


    ret = binary_search(a, 5)
    print(ret)

    ret = binary_search(a, 6)
    print(ret)

    ret = binary_search(a, 242)
    print(ret)

    ret = binary_search(a, 823)
    print(ret)

    ret = binary_search(a, 8)
    print(ret)