Myers common subsequence

myers-common-subsequence · version 1.0.0 · Sequences & diffs · free, no key needed

Return a canonical indexed LCS witness derived from bounded Myers search, or null when its cap is exceeded.

Use when you need to: find canonical longest common subsequence · return indexed LCS witness · bounded Myers common subsequence.

Decide before calling

Read the versioned contract and the supported scope below. Reuse myers-common-subsequence@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use myers-common-subsequence@1.0.0 for find canonical longest common subsequence. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

• find canonical longest common subsequence
• return indexed LCS witness
• bounded Myers common subsequence
• match equal tokens between sequences
• compute LCS with a distance cap
• prove a common subsequence with indices

Not supported

• returning edit operations
• substring or approximate string matching

Behavior

• The witness contains the equal steps of the canonical Myers shortest edit script with zero-based indices.
• Implements Myers 1986; deletion wins frontier ties and therefore fixes one LCS when several exist.

Input

• a (array of string, required): max items 256; each max length 1024
• b (array of string, required): max items 256; each max length 1024
• max_distance (integer, required): min 0; max 512

Output

• reference (constant "Myers 1986; RFC 3284 section 5", required)
• version (constant "1.0.0", required)
• within_limit (boolean, required)
• distance (integer or null, required): min 0; max 512
• matches (array or null, required): max items 256

Limits

• max input bytes: 131072
• max items: 256
• max item bytes: 1024
• max distance: 512
• max iterations: 263169
• max output items: 512

Example

Request input:

{
  "a": [
    "A",
    "B"
  ],
  "b": [
    "A",
    "C"
  ],
  "max_distance": 2
}

Response:

{
  "result": {
    "reference": "Myers 1986; RFC 3284 section 5",
    "version": "1.0.0",
    "within_limit": true,
    "distance": 2,
    "matches": [
      {
        "a_index": 0,
        "b_index": 0,
        "value": "A"
      }
    ]
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "myers-common-subsequence",
  "version": "1.0.0",
  "input": {
    "a": [
      "A",
      "B"
    ],
    "b": [
      "A",
      "C"
    ],
    "max_distance": 2
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/myers-common-subsequence/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"a":["A","B"],"b":["A","C"],"max_distance":2}'

The machine-readable contract is at /v1/tools/myers-common-subsequence/versions/1.0.0.

CLI

node cli.mjs run myers-common-subsequence 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• Myers distance bounded: Compute Myers insert/delete distance up to a caller cap, returning null predictably when the cap is exceeded.
• Myers diff bounded: Produce a canonical Myers edit script within a caller distance cap, or a deterministic over-cap result.
• Sequence LCS: Compute the longest common subsequence of two bounded sequences from the Myers shortest edit script.
• Sequence longest common substring: Find the longest contiguous common subarray of two bounded sequences.
• Sequence edit script: Compute the Myers shortest edit script between two bounded sequences, with keep/delete/insert counts.
• Sequence index map: Map each left-sequence index to a kept right index, or null if deleted, and list inserted right indices.