Leetcode: Number of Matching Subsequences

Number of Matching Subsequences



Similar Problems:


Given string S and a dictionary of words words, find the number of words[i] that is a subsequence of S.

Example :

Input: 
S = "abcde"
words = ["a", "bb", "acd", "ace"]
Output: 3
Explanation: There are three words in words that are a subsequence of S: "a", "acd", "ace".

Note:

  • All words in words and S will only consists of lowercase letters.
  • The length of S will be in the range of [1, 50000].
  • The length of words will be in the range of [1, 5000].
  • The length of words[i] will be in the range of [1, 50].

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


## Blog link: https://code.dennyzhang.com/number-of-matching-subsequences
## Basic Ideas:
## Complexity: Time O(n*m), Space O(1)
class Solution:
    def numMatchingSubseq(self, S, words):
        """
        :type S: str
        :type words: List[str]
        :rtype: int
        """
        res = 0
        ok_set = set([])
        invalid_set = set([])
        for word in words:
            # avoid duplicate calculation
            if word in ok_set:
                res += 1
                continue

            if word in invalid_set: continue

            index = 0
            for ch in S:
                if ch == word[index]: index += 1
                if index == len(word):
                    res += 1
                    break

            if index != len(word):
                invalid_set.add(word)
            else:
                ok_set.add(word)
        return res
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