2486. Append Characters to String to Make Subsequence

Problem Statement

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.

Examples

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

• Both s and t consist of only lowercase English letters.
• (1 \leq s.length, t.length \leq 10^4)

Solution

func appendCharacters(s string, t string) int {
    j := 0
	for i := 0; i < len(s) && j < len(t); i++ {
		if s[i] == t[j] {
			j++
		}
	}
	return len(t) - j
}