python算法：Longest Common Subsequence

Write a function called LCS that accepts two sequences and returns the longest subsequence common to the passed in sequences.

Subsequence
A subsequence is different from a substring. The terms of a subsequence need not be consecutive terms of the original sequence.

Example subsequence
Subsequences of "abc" = "a", "b", "c", "ab", "ac", "bc" and "abc".

LCS examples
lcs( "abcdef" , "abc" ) => returns "abc"
lcs( "abcdef" , "acf" ) => returns "acf"

lcs( "132535365" , "123456789" ) => returns "12356"

我的解法：

def lcs(x, y):
    a=''
    x_l=list(x)
    for i in y:
        if i in x_l:
            a+=i
            x_l[:(x_l.index(i)+1)]=[]
    return a

其他解法：

def lcs(x, y):
  res=[]
  i=0
  for item in y:
     if item in x[i:]:
        res+=[item]
        i=x.index(item)+1
  return "".join(res)