Python 如何使用分治方法解决FindMaximum子阵列的重复误差?
这是我对findMaximumSubarray的解决方案,我遵循CLRS伪代码算法,我得到了这个递归错误,我试图找出原因,但我一无所获 我无法理解递归的这一部分,第一行是找到左除数组,直到到达一个元素的基本情况,然后我的大脑开始崩溃,我无法想象接下来会发生什么Python 如何使用分治方法解决FindMaximum子阵列的重复误差?,python,algorithm,divide-and-conquer,clrs,Python,Algorithm,Divide And Conquer,Clrs,这是我对findMaximumSubarray的解决方案,我遵循CLRS伪代码算法,我得到了这个递归错误,我试图找出原因,但我一无所获 我无法理解递归的这一部分,第一行是找到左除数组,直到到达一个元素的基本情况,然后我的大脑开始崩溃,我无法想象接下来会发生什么 leftLow, leftHigh, leftSum = FindMaxSubarray(array, low, mid) rightLow, rightHigh, rightSum = FindMaxSubarray(array,
leftLow, leftHigh, leftSum = FindMaxSubarray(array, low, mid)
rightLow, rightHigh, rightSum = FindMaxSubarray(array, mid, high)
crossLow, crossHigh, crossSum = MaxCrossSubarray(array, low, mid, high)
这就是全部代码
array = [0,1,-2,3,4,-2, 5, -1, 10, -2 ,11,9, -5, -10, 12]
low = 0
high = len(array)
mid = len(array)//2
def MaxCrossSubarray(array, low, mid, high):
sum = 0
left_sum = float('-inf')
for i in range(mid, low, -1):
sum = sum+array[i]
if sum > left_sum:
left_sum = sum
max_left = i
right_sum = float('-inf')
sum = 0
for i in range(mid+1, high):
sum = sum+array[i]
if sum > right_sum:
right_sum = sum
max_right = i
return (max_left, max_right, left_sum+right_sum)
def FindMaxSubarray(array, low, high):
if high == low :
return (low, high, array[low])
else:
mid = (high+low)//2
leftLow, leftHigh, leftSum = FindMaxSubarray(array, low, mid)
rightLow, rightHigh, rightSum = FindMaxSubarray(array, mid, high)
crossLow, crossHigh, crossSum = MaxCrossSubarray(array, low, mid, high)
if leftSum >= rightSum and leftSum >=crossSum:
return (leftLow, leftHigh, leftSum)
elif rightSum >= leftSum and rightSum >=crossSum:
return (rightLow, rightHigh, rightSum)
else:
return (crossLow, crossHigh, crossSum)
low, high, sum = FindMaxSubarray (array, low, high)
上面代码中的思想是,您正在查找数组右侧、左侧和交叉和的子数组的最大值。正如您在问题中所解释的,第一行是查找divide left数组,直到到达一个元素的基本大小写。这是正确的,同样的逻辑适用于其他部件
递归问题源于这一行
rightLow, rightHigh, rightSum = FindMaxSubarray(array, mid, high)
其中mid=0
和high=1
,这会导致递归错误,因为在这些值下,以下值始终为假
if high == low :
return (low, high, array[low])
要解决递归问题,只需更改为
rightLow, rightHigh, rightSum = FindMaxSubarray(array, mid+1, high)
这可以确保满足返回条件,从而防止递归错误
更改后,您的MaxCrossSubArray
似乎在逻辑上不正确,运行时会出现以下错误
UnboundLocalError:赋值前引用的局部变量“max_right”
调查一下,看看你是否能解决它
N.B:已知CLR包含一些错误,并且相对较旧。因此,我建议你不要坚持使用相同的解决方案,而是寻找其他的可能性。请参阅示例。请务必查看我的答案,并让我知道它是否有助于范围内的i(中,低-1,-1):
low-1是我的错误,因为range
达到1而不是0,并停止我的低值为0。
rightLow, rightHigh, rightSum = FindMaxSubarray(array, mid+1, high)