3018. Make String a Subsequence Using Cyclic Increments

Medium
Two Pointers
String

Description

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.

Hints

Hint 1
<div class="_1l1MA">Consider the indices we will increment separately.</div>
Hint 2
<div class="_1l1MA">We can maintain two pointers: pointer <code>i</code> for <code>str1</code> and pointer <code>j</code> for <code>str2</code>, while ensuring they remain within the bounds of the strings.</div>
Hint 3
<div class="_1l1MA">If both <code>str1[i]</code> and <code>str2[j]</code> match, or if incrementing <code>str1[i]</code> matches <code>str2[j]</code>, we increase both pointers; otherwise, we increment only pointer <code>i</code>.</div>
Hint 4
<div class="_1l1MA">It is possible to make <code>str2</code> a subsequence of <code>str1</code> if <code>j</code> is at the end of <code>str2</code>, after we can no longer find a match.</div>

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