2825

2825. Make String a Subsequence Using Cyclic Increments (Medium)

You are given two 0-indexed strings str1 and str2.

In an operation, you select a set of indices in str1, and for each index i in the set, increment str1[i] to the next character cyclically. That is 'a' becomes 'b', 'b' becomes 'c', and so on, and 'z' becomes 'a'.

Return true if it is possible to make str2 a subsequence of str1 by performing the operation at most once, and false otherwise.

Note: A subsequence of a string is a new string that is formed from the original string by deleting some (possibly none) of the characters without disturbing the relative positions of the remaining characters.

 

Example 1:

Input: str1 = "abc", str2 = "ad"
Output: true
Explanation: Select index 2 in str1.
Increment str1[2] to become 'd'. 
Hence, str1 becomes "abd" and str2 is now a subsequence. Therefore, true is returned.

Example 2:

Input: str1 = "zc", str2 = "ad"
Output: true
Explanation: Select indices 0 and 1 in str1. 
Increment str1[0] to become 'a'. 
Increment str1[1] to become 'd'. 
Hence, str1 becomes "ad" and str2 is now a subsequence. Therefore, true is returned.

Example 3:

Input: str1 = "ab", str2 = "d"
Output: false
Explanation: In this example, it can be shown that it is impossible to make str2 a subsequence of str1 using the operation at most once. 
Therefore, false is returned.

 

Constraints:

• 1 <= str1.length <= 105
• 1 <= str2.length <= 105
• str1 and str2 consist of only lowercase English letters.

Companies: Amazon

Related Topics:
Two Pointers, String

Similar Questions:

• Is Subsequence (Easy)

Hints:

• Consider the indices we will increment separately.
• We can maintain two pointers: pointer i for str1 and pointer j for str2, while ensuring they remain within the bounds of the strings.
• If both str1[i] and str2[j] match, or if incrementing str1[i] matches str2[j], we increase both pointers; otherwise, we increment only pointer i.
• It is possible to make str2 a subsequence of str1 if j is at the end of str2, after we can no longer find a match.

Solution 1.

// OJ: https://leetcode.com/problems/make-string-a-subsequence-using-cyclic-increments
// Author: github.com/lzl124631x
// Time: O(M + N)
// Space: O(1)
class Solution {
public:
    bool canMakeSubsequence(string s, string t) {
        int i = 0, j = 0, M = s.size(), N = t.size();
        for (; i < M && j < N; ++i) {
            if (s[i] == t[j] || ('a' + (s[i] - 'a' + 1) % 26) == t[j]) ++j;
        }
        return j == N;
    }
};