Question

def binary_search(li, targetValue):
   low, high = 0, len(li)
   while low <= high:
        mid = (high - low)/2 + high
        if li[mid] > targetValue:
             low = mid - 1;
        elif li[mid] < targetValue:
             high = mid + 1;
        elif li[mid] == targetValue:
             return "we found it!"
   print start, end 
   return False

我几乎肯定它有效。它在数组中存在targetValue时有效，但是当你要求它在给定元素之外找到一个值时，它就不再起作用了......

有谁知道为什么？

Answer 1

来自http://docs.python.org/2/library/bisect.html

import bisect
bisect.bisect_left(li, targetValue)

Answer 2

我不确定你要打印的是什么，但是我看到那个功能可能存在一些不当行为。尝试这样的事情：

# binary search for list with desending values
def binary_search(li, targetValue):
    low, high = 0, len(li) - 1  # min & max index
    while low <= high:          # loop til high & low switch
        mid = (high + low) / 2  # midpoint (rounds down)
        if li[mid] > targetValue: low = mid + 1     # confine to upper half
        elif li[mid] < targetValue: high = mid - 1  # confine to lower half
        elif li[mid] == targetValue: return mid     # found it!
    return None  # nothing to return (low/high switched, so it wasn't found)

如果targetValue位于li，则会返回匹配的索引，否则返回None。使用如下：

li = [10000, 1000, 100, 10, 1]

if binary_search(li, 500) is None: print '500 not found!'
else: print '500 found!'

i = binary_search(li, 10)
if i is None: print '10 not found!'
else: print 'Found 10 at index ' + str(i) + '!'

那会输出：

500 not found!
Found 10 at index 3!

对于加入li，只需切换<和>：

def binary_search(li, targetValue):
    low, high = 0, len(li) - 1
    while low <= high:
        mid = (high + low) / 2
        if li[mid] < targetValue: low = mid + 1
        elif li[mid] > targetValue: high = mid - 1
        elif li[mid] == targetValue: return mid
    return None

不打印输出？蟒蛇

2 个答案: