Lua二分答案：判定单调的最优解搜索

-- 错误：从低星逐级试到失败，级高时白跑大半程
local star = 0
while canReach(star + 1, stones) do
    star = star + 1
end

local function canReach(star, stones, perStar)
    return stones >= star * perStar
end
local function maxStar(stones, perStar, cap)
    local lo, hi = 0, cap
    while lo < hi do
        local mid = math.ceil((lo + hi) / 2)
        if canReach(mid, stones, perStar) then
            lo = mid
        else
            hi = mid - 1
        end
    end
    return lo
end
local label = panel:getChildByName("starText")
label:setString(tostring(maxStar(800, 20, 60)))