2486. Append Characters to String to Make Subsequence

Medium
You are given two strings s and t consisting of only lowercase English letters.
Return the minimum number of characters that need to be appended to the end of s so that t becomes a subsequence of s.
A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.
Example 1:
Input: s = "coaching", t = "coding"
Output:
4
Explanation:
Append the characters "ding" to the end of s so that s = "coachingding".
Now, t is a subsequence of s ("coachingding").
It can be shown that appending any 3 characters to the end of s will never make t a subsequence.
Example 2:
Input: s = "abcde", t = "a"
Output:
0
Explanation:
t is already a subsequence of s ("abcde").
Example 3:
Input: s = "z", t = "abcde"
Output:
5
Explanation:
Append the characters "abcde" to the end of s so that s = "zabcde".
Now, t is a subsequence of s ("zabcde").
It can be shown that appending any 4 characters to the end of s will never make t a subsequence.
Constraints:
  • 1 <= s.length, t.length <= 105
  • s and t consist only of lowercase English letters.

解題

func appendCharacters(s string, t string) int {
spointer, tpointer := 0, 0
​
for spointer < len(s) && tpointer < len(t) {
if t[tpointer] == s[spointer] { // 找到相同的字元,可以找 t 的下一個字元了
tpointer++
spointer++
} else {
spointer++ // 在 s 繼續尋找 t[tpointer]
}
}
​
return len(t) - tpointer
}