LeetCode 75 Level 1 — Is Subsequence

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Problem

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).

Examples

• 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.

Solution

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        if not s:
            return True
        if not t:
            return False
        
        sleft, sright = 0, len(s)
        tleft, tright = 0, len(t)
        
        while sleft < sright and tleft < tright:
            if s[sleft] == t[tleft]:
                sleft += 1
            tleft += 1
        
        return sleft == len(s)

Time and Space Complexity

• Time Complexity: O(t). Given t is the number of elements in string t .
• Space Complexity: O(1). No auxiliary memory space used.

Takeaways

Thank you for reading this short problem solving question. If anyone knows a better or faster time complexity to solve this question, feel free to comment and feedback. Peace! ✌️

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