二分法查找

def binary_search(alist, item):
    first = 0
    last = len(alist) - 1
    while first <= last:
        midpoint = (first + last) // 2
        if alist[midpoint] == item:
            return True
        elif item < alist[midpoint]:
            last = midpoint - 1
        else:
            first = midpoint + 1
    return False

testlist = [0, 1, 2, 8, 13, 17, 19, 32, 42, ]
print(binary_search(testlist, 3))
print(binary_search(testlist, 13))

# 递归使用二分法查找数据
def binary_search(alist, item):
    if len(alist) == 0:
        return False
    else:
        midpoint = len(alist)//2

        if alist[midpoint]==item:
          return True

        else:
          if item < alist[midpoint]:
            return binary_search(alist[:midpoint],item)
            #从开始到中间
          else:#item元素大于alist[midpoint]
            return binary_search(alist[midpoint+1:],item)
            #从中间到最后

testlist = [0, 1, 2, 8, 13, 17, 19, 32, 42,]
print(binary_search(testlist, 3))
print(binary_search(testlist, 13))