How to detect identical part (s) inside a string?

Question

I am trying to break down a decoding algorithm algorithm, which is required for smaller questions. This is part I.

Question:

• two lines: s1 and s2
• part s1 is identical to part s2
• space is separator
• How to extract identical part (s)?

example 1:

s1 = "12 November 2010 - 1 visitor"
s2 = "6 July 2010 - 100 visitors"

the identical parts are "2010", "-", "1" and "visitor"

Example 2:

s1 = "Welcome, John!"
s2 = "Welcome, Peter!"

the identical parts are "Welcome," and "!"

Example 3: (to clarify the "!" Example)

s1 = "Welcome, Sam!"
s2 = "Welcome, Tom!"

the identical parts are "Welcome," and "m!"

Python and Ruby are preferred. Thanks

Answer 1

EDIT: Updated this example to work with all examples, including # 1:

def scan(s1, s2):
    # Find the longest match where s1 starts with s2
    # Returns None if no matches
    l = len(s1)
    while 1:
        if not l:
            return None
        elif s1[:l] == s2[:l]:
            return s1[:l]
        else:
            l -= 1

def contains(s1, s2):
    D = {} # Remove duplicates using a dict
    L1 = s1.split(' ')
    L2 = s2.split(' ')

    # Don't add results which have already 
    # been processed to satisfy example #1!
    DProcessed = {}

    for x in L1:
        yy = 0
        for y in L2:
            if yy in DProcessed:
                yy += 1
                continue

            # Scan from the start to the end of the words
            a = scan(x, y)
            if a: 
                DProcessed[yy] = None
                D[a] = None
                break

            # Scan from the end to the start of the words
            a = scan(x[::-1], y[::-1])
            if a: 
                DProcessed[yy] = None
                D[a[::-1]] = None
                break
            yy += 1

    return list(D.keys())

print contains("12 November 2010 - 1 visitor",
               "6 July 2010 - 100 visitors")
print contains("Welcome, John!",
               "Welcome, Peter!")
print contains("Welcome, Sam!",
               "Welcome, Tom!")

What outputs:

['1', 'visitor', '-', '2010']
['Welcome,', '!']
['Welcome,', 'm!']

Answer 2

For example, 1

>>> s1 = 'November 2010 - 1 visitor'
>>> s2 = '6 July 2010 - 100 visitors'
>>> 
>>> [i for i in s1.split() if any(j for j in s2.split() if i in j)]
['2010', '-', '1', 'visitor']
>>>

For both

>>> s1 = "Welcome, John!"
>>> s2 = "Welcome, Peter!"
>>> [i for i in s1.replace('!',' !').split() if any(j for j in s2.replace('!',' !').split() if i in j)]
['Welcome,', '!']
>>>

. , , 3, OP

Answer 3

s1 = "12 November 2010 - 1 visitor"
s2 = "6 July 2010 - 100 visitors"
l1 = s1.split()
for item in l1:
   if item in s2:
      print item

.

, ( ! 2), Python, re.split() .

, , - ( 1234 1234, 123, 234, 12, 23, 34, 1, 2, 3 4, .

Answer 4

Ruby:

def start_similar(i, j)
    front = ''
    for ix in (0...([i.size, j.size].min))
      if i[ix] == j[ix] then
        front += i[ix].chr
      else
        break
      end
    end
    return front
end

def back_similar(i, j)
    back = ''
    for ix in (0...([i.size, j.size].min)).to_a.reverse
      dif = i.size < j.size ? j.size - i.size : i.size - j.size
      ci = i[ i.size < j.size ? ix : ix + dif ]
      cj = j[ i.size > j.size ? ix : ix + dif ]
      if ci == cj then
        back = ci.chr + back
      else
        break
      end
    end
    return back
end

def scan(x, y)
    a, b = x.split(' '), y.split(' ')
    result = []
    for i in a do
      for j in b do
        result << start_similar(i, j)
        result << back_similar(i, j)
      end
    end
    return result.uniq.select do |r| not r.empty? end
end

puts scan(
    "12 November 2010 - 1 visitor",
    "6 July 2010 - 100 visitors"
).inspect
# ["1", "2010", "0", "-", "visitor"]

puts scan(
    "Welcome, John!",
    "Welcome, Peter!"
).inspect
# ["Welcome,", "!"]

puts scan(
    "Welcome, Sam!",
    "Welcome, Tom!"
).inspect
# ["Welcome,", "m!"]