Single Substitution Witness
Witness exactly one changed UTF-16 unit between equal-length strings; zero or multiple changes yield null, not a fuzzy distance.
Description
Witness exactly one changed UTF-16 unit between equal-length strings; zero or multiple changes yield null, not a fuzzy distance.
A single-substitution witness is one differing position between equal-length strings. Insertions and deletions need different tests.
When to use this tool
Witness exactly one changed UTF-16 unit between equal-length strings; zero or multiple changes yield null, not a fuzzy distance.
- Prepare the supplied left, right 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 left, right. 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.index. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
For strings at most 128 UTF-16 code units, collect unequal positions when lengths match. Return the index only for exactly one difference, otherwise null.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| left | left. | Text; at most 8,192 UTF-16 code units, subject to the grammar above |
| right | right. | 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.index | The index value under the stated formula or text convention. |
{
"input": {
"left": "abc",
"right": "axc"
},
"output": {
"result": {
"index": 1
}
}
}Limitations and assumptions
- Equal strings also return null. Unicode normalization, code-point alignment and grapheme-aware edits are not performed.
- 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 Substitution Positions
Bounded UTF-16 string palindrome single substitution positions; exact code-unit matching, no Unicode normalization or grapheme inference.
- Single Insertion Witness
Return all insertion positions in the right string witnessing exactly one inserted UTF-16 unit from the left; repeated-unit ambiguities are retained.