Lua缺失编号：求和差值一步定位

local function findMissing(t, n)
    local seen = {}
    for _, v in ipairs(t) do seen[v] = true end
    for i = 1, n do
        if not seen[i] then return i end   -- 建表再扫，多花一遍
    end
end

local function findMissing(t, n)
    local expect = n * (n + 1) / 2   -- 理论总和闭式
    local actual = 0
    for _, v in ipairs(t) do
        actual = actual + v
    end
    return expect - actual           -- 差值即缺失编号
end
sendmsg(actor, 1, "缺失编号 "
    .. findMissing({1, 2, 4, 5}, 5))