392. Is Subsequence

Question

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.
A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).
 
Example 1:
Input: s = "abc", t = "ahbgdc"
Output: true
Example 2:
Input: s = "axc", t = "ahbgdc"
Output: false

Constraints:

0 <= s.length <= 100
0 <= t.length <= 104
s and t consist only of lowercase English letters.

Follow up: Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 109, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?

Prakash Sellathurai · Accepted Answer

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        #  s = "abc", t = "ahbgdc"
        #  count = 0
        #  i ..t -> loop
        #   j .. s
        #   if  char at i matches j
        #      j += 1
        #  return j == len(s)
        #  
        #  i = 0 ; j= 0 match  j += 1
        #  i =1 ; f
        #  i =2 ; t j =2
        #  i =3 ; f
        #  i =4 ; f
        #  i =5 l; t  j = 3
        cnt = 0
        for text  in t:
            if cnt < len(s) and text  == s[cnt]:
                cnt += 1
        return cnt == len(s)