python - 关于在列表中查找子序列的代码不返回任何内容

Question

此代码应该返回“words”列表中存在的最长字符串子序列(如果可以从 S 中删除一些字符(可能为零)以形成 W，而无需重新排序，则单词 W 是 S 的子序列其余字符)。但它对任何输入值都返回 None ，我不明白为什么。有什么建议吗？

string = input()
words = (input()).split()
def longest_subsequence (string, words):
  words = list(words)
  max_length = 0
  max_sub = ""
  for i in range(len(words)):
    ind = i
    isSubsequence = True
    for j in words[i]:
      if j == string[ind]:
        ind +=1
      else:
        isSubsequence = False
        break
    if isSubsequence and max_length < len(words[i].split()):
      max_length = len(words[i].split())
      max_sub = words[i]
  return max_sub
print (longest_subsequence(string, words))```

Answer 1

这是你出错的地方:

if isSubsequence and max_length < len(words[i].split()):
      max_length = len(words[i].split())
      max_sub = words[i]

这个条件语句只执行一次，因为最初 isSubsequence是真的并且 max_length为零。所以max_sub仅当子序列是单词列表中的第一个单词时才返回。对于其他迭代max_length < len(words[i].split()) len(words[i].split()) 永远不会成立总是返回 1。你应该尝试这个:

string = input()
words = (input()).split()
def longest_subsequence (string, words):
  words = list(words)
  max_length = 0
  max_sub = ""
  for i in range(len(words)):
    ind = 0
    isSubsequence = True
    for j in words[i]:
      if j == string[ind]:
        ind +=1
      else:
        isSubsequence = False
        break
    if isSubsequence and len(words[i]) > max_length:
      max_length = len(words[i].split())
      max_sub = words[i]
  return max_sub
print (longest_subsequence(string, words))