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
}