Description
Return the unique undirected node path through the lowest common ancestor; different components have null path.
A parent-record forest represents each node by an exact string ID and a parent ID or null for a root. Depth counts edges toward a root; subtree height counts edges toward the deepest descendant. Node order, identity, cycles and missing references are separate properties that must be checked before structural transformations.
Return the unique undirected node path through the lowest common ancestor; different components have null path.
When to use this tool
Use this tool to return the unique undirected node path through the lowest common ancestor; different components have null path.
How to use the tool and how it works
- Enter parentsJson, left, right using the definitions below. Serialize JSON text fields in the decoded shape shown below.
- Run the operation. Resolve input-format errors before interpreting an output.
- Read result.path, using the stated boundary, ordering, sign and absence conventions.
Build both self-first ancestor chains, locate the first left-chain node shared by the right chain, and join the left ascent through that ancestor to the reversed right ascent. Return null for separate components.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| parentsJson | JSON array of {id,parent} records. id is an exact string; parent is another exact ID or null for a root. | Text, at most 8,192 UTF-16 code units; narrower grammar/range rules also apply. |
| left | Existing left endpoint node ID. | Text, at most 8,192 UTF-16 code units; narrower grammar/range rules also apply. |
| right | Existing right endpoint node ID. | Text, at most 8,192 UTF-16 code units; narrower grammar/range rules also apply. |
These decoded structures show the examples inside JSON text fields. Supply their serialized JSON strings as input.
{
"parentsJson": [
{
"id": "a",
"parent": null
},
{
"id": "b",
"parent": "a"
},
{
"id": "c",
"parent": "a"
},
{
"id": "d",
"parent": "b"
}
]
}| Output field | Interpretation |
|---|---|
| result | Object containing the fields below. |
| result.path | Left-to-right node path through the lowest common ancestor, or null for separate components. |
{
"input": {
"parentsJson": "[{\"id\": \"a\", \"parent\": null}, {\"id\": \"b\", \"parent\": \"a\"}, {\"id\": \"c\", \"parent\": \"a\"}, {\"id\": \"d\", \"parent\": \"b\"}]",
"left": "d",
"right": "c"
},
"output": {
"result": {
"path": [
"d",
"b",
"a",
"c"
]
}
}
}Limitations and assumptions
- Both endpoint IDs must exist. The shared ancestor appears once in the left-to-right path.
- Structural operations require distinct node IDs, existing non-null parent IDs and no parent cycles; audit tools explicitly state when they accept incomplete structure. Multiple roots are allowed. Matching is exact and case-sensitive.
- Every declared outer field is required and unknown outer fields are rejected. Strings and JSON text have size limits, lists are bounded to 128 entries, and JSON nesting/node counts are bounded. Tighter operation-specific bounds stated above take precedence.
- Ordinary numeric outputs must be finite and within safe-integer magnitude. Exact large lengths/counts use decimal strings. Original record indexes and code-unit positions are zero-based; span ends are exclusive unless stated otherwise.
Alternative or Complementary methods
Use identity and cycle audits to inspect incomplete records, then structural operations on complete forests. Preserve sibling order explicitly when exchanging traversal results with another tree format.
References
Similar or alternative tools
- Parent Forest Ancestor Chain
Explicit complete acyclic parent forests with exact unique string node IDs and null roots; return strict ancestors nearest-first, excluding the query node; unknown IDs reject.
- Parent Forest Child Index
Explicit complete acyclic parent forests with exact unique string node IDs and null roots; index every node’s direct children in source order, retaining leaf nodes with empty lists.