Lua前缀和：区间求和的预计算

-- 错误：每次询问都现场累加
local function rangeSum(a, l, r)
    local s = 0
    for i = l, r do s = s + a[i] end
    return s
end

local function buildPrefix(a)
    local s = {0}
    for i = 1, #a do
        s[i] = s[i - 1] + a[i]
    end
    return s
end
local function query(s, l, r)
    return s[r] - s[l - 1]
end
local p = getplayerbyname("pre01")
local exp = buildPrefix({100, 200, 300, 400, 500})
sendmsg(p, 1, query(exp, 2, 4))