Graph BFS Shortest Path

Build an undirected, unweighted graph from an edge list and find the
shortest path (minimum number of edges) between two nodes using BFS.

Graph class

class Graph {
  addEdge(u, v)            // register undirected edge u ↔ v
  bfs(source, target)      // → hop count, or -1 if unreachable
}

Store adjacency lists in a Map<string, string[]>.

solve(edges, source, target) builds the graph, then returns bfs(source, target).

Examples

// Direct edge
solve([['A','B'],['B','C'],['A','C']], 'A', 'C')  → 1

// Two hops
solve([['A','B'],['B','C']], 'A', 'C')             → 2

// Disconnected
solve([['A','B'],['C','D']], 'A', 'C')             → -1

// Same node
solve([['A','B']], 'A', 'A')                        → 0

Constraints

• Node identifiers are strings.
• The graph may contain cycles — use a visited set to avoid infinite loops.
• If source has no edges at all and source ≠ target, return -1.