如何理解这个表达？

huangapple
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英文:

How to understand this expression?

问题

  1. error = (parityList.mapIndexed { i, parity -> parity.toInt() * (2.0.pow(i)).toInt() }).sum()

例如：我输入数字101

变量的值如下所示：

  1. parityList = [1, 0]
  2. i = 1
  3. error = 2

error = 2 是如何计算的呢？可以使用以下示例来解释执行顺序：

程序代码：

  1. val input = "101"
  2. val data = input.map { it.toString().toInt() }.toMutableList()
  3. val cList = mutableListOf<Int>()
  4. var c = 0
  5. val h = mutableListOf<Int>()
  6. val parityList = mutableListOf<Int>()
  8. for (k in data.indices) {
  9.     val p = 2.0.pow(c).toInt()
  10.     h.add(data[k])
  11.     if (p == (k + 1)) {
  12.         c++
  13.     }
  14. }
  16. for (parity in h.indices) {
  17.     val ph = 2.0.pow(parity.toDouble()).toInt()
  18.     if (ph == (parity + 1)) {
  19.         val startIndex = ph - 1
  20.         var i = startIndex
  21.         val toXor = mutableListOf<Int>()
  23.         while (i < h.size) {
  24.             val block = h.subList(i, i + ph)
  25.             toXor.addAll(block)
  26.             i += 2 * ph
  27.         }
  29.         for (z in 1 until toXor.size) {
  30.             h[startIndex] = h[startIndex] xor toXor[z]
  31.         }
  32.         parityList.add(h[parity])
  33.     }
  34. }
  35. parityList.reverse()
  37. val error = parityList.mapIndexed { i, parity -> parity * (2.0.pow(i)).toInt() }.sum()
  38. println("parityList = $parityList")
  39. println("parityList = ${parityList.reversed()}")
  40. println("i = $i")
  41. println("error = $error")
  42.    
  43. if (error == 0) {
  44.     println("在收到的Hamming码中没有错误")
  45. } else if (error >= data.size) {
  46.     println("错误无法检测到")
  47. } else {
  48.     println("错误位于第 $error 位")
  50.     if (data[error - 1] == 0) {
  51.         data[error - 1] = 1
  52.     } else if (data[error - 1] == 1) {
  53.         data[error - 1] = 0
  54.         println("修正Hamming码后： - ")
  55.     }
  56.     data.reverse()
  57.     val correctedData = data.joinToString("").toInt()
  58.     println(correctedData)
  59. }

我明白 for i, parityList in enumerate(parityList[::-1]) 函数是如何工作的，但是如何添加 int(parityList) * (2 ** i)？

  2. <details>
  3. <summary>英文:</summary>
  5. I am converting Hamming code from python to kotlin. And I almost did everything, but there is one expression that I do not understand.

error=sum(int(parity_list) * (2 ** i) for i, parity_list in enumerate(parity_list[::-1]))

  2. For example: I enter the number 101
  4. The value of the variables are obtained:

parity_list = [1,0]

i = 5

error = 2

  1. How come `error = 2`? Can you explain the execution sequence with an example?
  3. Program code:

coding=windows-1251

from traceback import print_tb

print('Введите полученный код Хэмминга')
d=input()
data=list(d)
data.reverse()
c,ch,j,r,error,h,parity_list,h_copy=0,0,0,0,0,[],[],[]

for k in range(0,len(data)):
p=(2**c)
h.append(int(data[k]))
h_copy.append(data[k])
if(p==(k+1)):
c=c+1

for parity in range(0,(len(h))):
ph=(2**ch)
if(ph==(parity+1)):

  1.         startIndex=ph-1
  2.         i=startIndex
  3.         toXor=[]
  5.         while(i&lt;len(h)):
  6.             block=h[i:i+ph]
  7.             toXor.extend(block)
  8.             i+=2*ph
  10.         for z in range(1,len(toXor)):
  11.             h[startIndex]=h[startIndex]^toXor[z]
  12.         parity_list.append(h[parity])
  13.         ch+=1

parity_list.reverse()

print('parity_list = ', parity_list)
print('parity_list = ', parity_list[::-1])
print('i = ', i)
error=sum(int(parity_list) * (2 ** i) for i, parity_list in enumerate(parity_list[::-1]))
print("error = ", error)

if((error)==0):
print('В полученном коде Хэмминга нет ошибок')

elif((error)>=len(h_copy)):
print('Ошибка не может быть обнаружена')

else:
print('Error is in',error,'bit')

  1.     if(h_copy[error-1]==&#39;0&#39;):
  2.         h_copy[error-1]=&#39;1&#39;
  4.     elif(h_copy[error-1]==&#39;1&#39;):
  5.         h_copy[error-1]=&#39;0&#39;
  6.         print(&#39;После исправления код Хэмминга: - &#39;)
  7.     h_copy.reverse()
  8.     print(int(&#39;&#39;.join(map(str, h_copy))))
  2. I understand how the function `for i, parity_list in enumerate(parity_list[::-1])` works, but how to add this `int(parity_list) * (2 ** i)`?
  4. </details>
  7. # 答案1
  8. **得分**: 0
  10. ```python
  11. # 定义列表
  12. parity_list = [1, 0]
  13. # 反转列表
  14. reveresed_parity_list = parity_list[::-1]
  15. # 将错误输出定义为0
  16. error = 0
  17. # 遍历每个元素，获取索引和值，其中i是索引，parity_list_value是值
  18. for i, parity_list_value in enumerate(reveresed_parity_list):
  19.     # 如果i = 0，那么2^0 = 1，按照任何值的0次方的规则
  20.     error += int(parity_list_value) * (2 ** i)
英文: 
  1. # Define the list
  2. parity_list = [1, 0];
  3. # reverse the list
  4. reveresed_parity_list = parity_list[::-1]
  5. # define error output as 0
  6. error = 0
  7. # loop through each element, getting the index and the value where i is the index and parity_list_value is the value
  8. for i, parity_list_value in enumerate(reveresed_parity_list):
  9.     # if i = 0 then 2^0 = 1 as the rule for any value to the exponent of 0
  10.     error += int(parity_list_value) * (2 ** i)

huangapple
  • 本文由 发表于 2023年2月27日 01:32:14
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  • python
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