【安全加密】异常交易图谱：资金流向的环路检测

---交易流水建图：账号为点，流转为边
function Graph.build(windowHours)
    local g = { edges = {}, adj = {} }
    local since = os.time() - windowHours * 3600
    for _, t in ipairs(Ledger.since(since)) do
        local e = { from = t.from, to = t.to,
            amt = t.amt, at = t.at, kind = t.kind }
        g.edges[#g.edges + 1] = e
        g.adj[e.from] = g.adj[e.from] or {}
        table.insert(g.adj[e.from], e)
    end
    return g
end

---DFS 找环：路径回到起点即成环
function Graph.findCycle(g, start, node, depth, path, out)
    if depth > 3 then return end
    path[#path + 1] = node
    for _, e in ipairs(g.adj[node] or {}) do
        if e.to == start and depth >= 2 then
            out[#out + 1] = { path = { unpack(path) },
                amt = Graph.sumEdges(g, path) }
        elseif not path marks(e.to) then
            Graph.findCycle(g, start, e.to, depth + 1, path, out)
        end
    end
    path[#path] = nil
end