Palindrome Single Substitution Positions
Bounded UTF-16 string palindrome single substitution positions; exact code-unit matching, no Unicode normalization or grapheme inference.
Description
Bounded UTF-16 string palindrome single substitution positions; exact code-unit matching, no Unicode normalization or grapheme inference.
Making a palindrome with exactly one character substitution differs from merely allowing at most one edit.
When to use this tool
Bounded UTF-16 string palindrome single substitution positions; exact code-unit matching, no Unicode normalization or grapheme inference.
- Prepare the supplied text fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter text. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.possible, result.positions. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Inspect mirrored code-unit pairs. For exactly one mismatched pair, return its two positions; for an already palindromic odd-length string, return its center. Otherwise positions is empty and possible false.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| text | text. | Text; at most 8,192 UTF-16 code units, subject to the grammar above |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.possible | Flag for possible under the exact condition described above. |
| result.positions | The positions list in the ordering and representation described above. |
{
"input": {
"text": "abca"
},
"output": {
"result": {
"possible": true,
"positions": [
1,
2
]
}
}
}Limitations and assumptions
- The center can change without breaking an odd palindrome. An already palindromic even-length string is not accepted for exactly one actual substitution; no replacement characters are generated.
- The string-analysis source text is bounded to 128 UTF-16 code units; offsets and lengths use those code units.
- All declared input fields are required and unexpected top-level fields are rejected. Numbers must be finite; lists are limited to 128 entries and ordinary text fields to 8,192 UTF-16 code units, with tighter limits where stated.
- JSON text inputs must parse within bounded nesting and size limits. Numeric outputs outside the safe finite range are rejected; large exact integer results use decimal strings. Indexes and half-open spans are zero-based unless a rank is explicitly described as one-based.
Alternative or Complementary methods
Use a code-point or grapheme-aware text method when the task concerns user-perceived characters. These bounded literal operations retain case and code-unit structure rather than normalizing linguistic text.
References
Similar or alternative tools
- Palindrome Single Deletion Indexes
Bounded UTF-16 string palindrome single deletion indexes; exact code-unit matching, no Unicode normalization or grapheme inference.
- Single Substitution Witness
Witness exactly one changed UTF-16 unit between equal-length strings; zero or multiple changes yield null, not a fuzzy distance.