2486. Append Characters to String to Make Subsequence
Description
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
andt
consist only of lowercase English letters.
Solutions
Solution 1: Two Pointers
We define two pointers $i$ and $j$, pointing to the first characters of strings $s$ and $t$ respectively. We iterate through string $s$, if $s[i] = t[j]$, then we move $j$ one step forward. Finally, we return $n - j$, where $n$ is the length of string $t$.
The time complexity is $O(m + n)$, where $m$ and $n$ are the lengths of strings $s$ and $t$ respectively. The space complexity is $O(1)$.
1 2 3 4 5 6 7 |
|
1 2 3 4 5 6 7 8 9 10 11 |
|
1 2 3 4 5 6 7 8 9 10 11 12 |
|
1 2 3 4 5 6 7 8 9 |
|
1 2 3 4 5 6 7 8 9 |
|