【安全加密】交易洗钱识别：资金流向的环路检测

-- 交易流水建图：源->目标 的金额累计
function FlowGraph.build(day)
    local g = {}
    for _, row in ipairs(TradeLog.load(day)) do
        local key = row.from .. ">" .. row.to
        g[key] = (g[key] or 0) + row.amount
    end
    return g
end

-- 递归回溯找环：起点回到起点即成环
function FlowGraph.findCycle(g, start, node, path, depth)
    if depth > 6 then return nil end
    for key, amount in pairs(g) do
        local from, to = key:match("^(.+%)>(.+)$")
        if from == node then
            if to == start and amount > 100000 then
                return path
            end
            local found = FlowGraph.findCycle(g, start, to, path .. ">" .. to, depth + 1)
            if found then return found end
        end
    end
    return nil
end