问题

Given two strings s and t, check if s is a subsequence of t.

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:

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 s = "abc", t = "ahbgdc"

Output:

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 true

Example 2:

Input:

1

 s = "axc", t = "ahbgdc"

Output:

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 false

 

Constraints:

  • 0 <= s.length <= 100
  • 0 <= t.length <= 104
  • s and t consist only of lowercase English letters.

 

Follow up: If 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?

解答：

从左到右逐个比较主字符串和子字符串

  • 相等时，同时移动主串和子字符串索引指向下一个字符
  • 不相等，仅移动主串索引指向下一个字符

如果发现子数组的索引已经移动到了数组的末尾，即等于字串长度，表明找到字符串。

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class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        sIdx = 0
        tIdx = 0
        while  sIdx < len(s) and tIdx <len(t):
            if s[sIdx] == t[tIdx]:
                sIdx += 1
            tIdx += 1
            
        return sIdx == len(s)

 

参考及引用

Photo by Erik Karits from Pexels