tree-rerooting

Included with Lifetime

$97 forever

Re-root an undirected tree from any node using DFS/BFS. Use when changing the point of view in a tree, finding paths between nodes, or reparenting tree structures.

Backend & APIs

What this skill does


## When to use

Re-rooting an undirected tree from a new node.

## Rules

- Build an undirected adjacency map (parent↔children become symmetric neighbor sets)
- Do DFS/BFS from the target node
- Every node you visit gets its parent set to the node you came from
- Its children become all neighbors minus that parent
- Path-between(a, b): re-root at a, then walk from b up parent pointers until you hit a
- If the target node is not in the tree, return None (not an error)
- NEVER mutate the original tree when re-rooting — build a fresh node structure
- ALWAYS keep the original tree intact so repeated from_pov calls work correctly

## Complexity

O(N) per re-root.

## Example

Path between a and b: build adjacency map, DFS from `a` as root, then walk from `b` up parent pointers to `a`. Always build a fresh structure — never mutate the original tree.

Files: 1

Size: 1.3 KB

Complexity: 10/100

Category: Backend & APIs

Source: https://github.com/knoopx/pi/tree/main/agent/skills/knowledge/tree-rerooting

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