[LeetCode] 392. Is Subsequence 풀이

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?

 

각 edge case에 대해서 분류해서 구현하면 다음과 같이 나온다.

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        idx = 0
        flag = False
        if not len(s) > 0:
            flag = True
            return flag

        if not len(t) > 0:
            flag = False
            return flag

        for i in range(len(s)):
            for j in range(idx, len(t)):
                if s[i] == t[j]:
                    idx = j + 1
                    break
            if i < (len(s)-1) and j == (len(t)-1):
                return flag
            elif i == (len(s)-1) and j == (len(t)-1) and s[i] != t[j]:
                return flag

        
        if i == (len(s)-1) and j <= (len(t)-1):
            flag = True
        return flag