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;
    }
}