Question

Write a Python function has_subsequence(a,s) that determines if the list (or string), a, contains s as a (not necessarily consecutive) subsequence.

Examples

• 'here we go again' contains 'we gain' as a subsequence.
• 'green eggs and ham sandwhiches' contains 'reggae' as a subsequence.

Your function should return an array of indices that shows the location of the elements of s in a. In the 'here we go again' example this array would contains [5,6,12,13,14,15].

If you can't find s as a subsequence of a, then you should return None.

Answer 1

# python code to check if a is subsequence of b

# Recursive Python program to check if a string is subsequence
# of another string

# Returns true if str1[] is a subsequence of str2[]. m is
# length of str1 and n is length of str2

# index stores indexes of string 1
index=[]
def isSubSequence(string1, string2, m, n):
   # Base Cases
   if m == 0: return True
   if n == 0: return False

   # If last characters of two strings are matching
   if string1[m-1] == string2[n-1]:
index.append(m-1)
       return isSubSequence(string1, string2, m-1, n-1)

   # If last characters are not matching
   return isSubSequence(string1, string2, m, n-1)

# Driver program to test the above function
string1 = "gksrek"
string2 = "geeksforgeeks"
m = len(string1)
n = len(string2)
if isSubSequence(string1, string2, m, n):
   print(index)
else:
   print "No"