【进阶实战】Lua前缀和：沙巴克防线任意区间战力的O(1)求和

local function rangeSum(a, i, j)
    local s = 0
    for k = i, j do s = s + a[k] end   -- 每查一次扫一段
    return s
end

local P = {0}
for i = 1, #POW do
    P[i] = P[i - 1] + POW[i]      -- 前缀和预计算
end
local function rangeSum(i, j)
    return P[j] - P[i - 1]        -- 一次减法出区间和
end
sendmsg(actor, 1, "沙巴克3到7段战力和 " .. rangeSum(3, 7))