Find Number of Subsequences in Word List using Python

Suppose we have a list of words and a string s, we have to find the number of strings in the words list that are subsequences of s.

So, if the input is like words = ["xz", "xw", "y"] s = "xyz", then the output will be 2, as "xz" and "y" are subsequences of "xyz".

To solve this, we will follow these steps −

• ans := 0
• d := an empty map
• for each word in words, do
  • insert word at the end of d[word[0]]
• for each c in s, do
  • l := d[c]
  • d[c] := a new list
  • for each word in l, do
    • if size of word is 1, then
      • ans := ans + 1
    • otherwise,
      • insert substring of word[from index 1 to end] at the end of d[word[1]]
• return ans

Let us see the following implementation to get better understanding −

Example 

Live Demo

from collections import defaultdict
class Solution:
   def solve(self, words, s):
      ans = 0

      d = defaultdict(list)
      for word in words:
         d[word[0]].append(word)

      for c in s:
         l = d[c]
         d[c] = []

         for word in l:
            if len(word) == 1:
               ans += 1
            else:
               d[word[1]].append(word[1:])
      return ans
ob = Solution()
words = ["xz", "xw", "y"]
s = "xyz"
print(ob.solve(words, s))

Input

["xz", "xw", "y"], "xyz"

Output

2