# 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):