2486. Append Characters to String to Make Subsequence

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# 題目敘述

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.

# 解題思路

# Solution

class Solution {

    public int appendCharacters(String s, String t) {

        int sIdx = 0, tIdx = 0, sLen = s.length(), tLen = t.length();

        while (sIdx < sLen && tIdx < tLen) {

            if (s.charAt(sIdx) == t.charAt(tIdx)) tIdx++;

            sIdx++;

        }

        return tLen - tIdx;

    }

}