2486

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.

Companies: Amazon

Related Topics:
Two Pointers, String, Greedy

Similar Questions:

• Is Subsequence (Easy)
• Minimum Operations to Make a Subsequence (Hard)

Solution 1. Two Pointers

// OJ: https://leetcode.com/problems/append-characters-to-string-to-make-subsequence
// Author: github.com/lzl124631x
// Time: O(M + N)
// Space: O(1)
class Solution {
public:
    int appendCharacters(string s, string t) {
        int M = s.size(), N = t.size(), i = 0, j = 0;
        while (i < M && j < N) {
            while (i < M && s[i] != t[j]) ++i;
            if (i < M) ++i, ++j;
        }
        return N - j;
    }
};