392. Is Subsequence

Tags: #twopointers #string #dynamicprogramming #easy

Problem Statement

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).

Input: s = "axc", t = "ahbgdc"
Output: false

Input: s = "abc", t = "ahbgdc"
Output: true

My approach

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

In this solution, first we check if the subsequent string is empty upon which it will be a subsequence no matter what. Then we loop over t, the string to be checked against and if r is less than the length of s (this prevents a list out of index exception) and the current element is same as s's rth item then, we increment r. Finally, we check if r is equal to the assumed subsequence length, returning True or False.

Personal Thoughts

This was a rather simple approach suggested by one of our classmates when I was thinking of a more complex one involving two loops.