7/3 每日一題(有s、t兩組字串,檢查t是否由s的子序列)

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?

class Solution:

    def isSubsequence(self, s: str, t: str) -> bool:

        '''使用雙指針'''

        i=0 #s的指針

        j=0 #t的指針

        while i<len(s) and j < len(t):

            if s[i] == t[j]:

                i+=1  #遇到相同母元素,繼續檢查下一項母元素

            j += 1

        return i == len(s)  #是否全部母元素依序存在