Is Subsequence

Intuition

• Check if the current character == the one you are at. If so, increase i by 1.
• When i reaches the end of s, then you have encountered an occurrence of each string you wish for in s, and it has occurred in t.

Runtime

$O(T)$ to go through each character in T

Code

Alternative 2

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        if not s:
            return True
 
        i = 0
        j = 0
 
        for j in range(len(t)):
            if i < len(s) and s[i] == t[j]:
                i += 1
 
        if i == len(s):
            return True
        return False

Alternative 1

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        i, s_len = 0, len(s)
        for j in range(len(t)):
            if i == s_len:
                return True
            if s[i] == t[j]:
                i += 1
 
        return i == s_len

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References

https://leetcode.com/problems/is-subsequence/