Lua区间覆盖：贪心选段的广告牌

local function sortSegs(segs)
    table.sort(segs, function(a, b)
        return a[1] < b[1]
    end)
    return segs
end

local function cover(segs, target)
    segs = sortSegs(segs)
    local start, used, i = 1, 0, 1
    while start <= target and i <= #segs do
        local far = start - 1
        while i <= #segs and segs[i][1] <= start do
            far = math.max(far, segs[i][2])
            i = i + 1
        end
        if far < start then return -1 end
        used = used + 1
        start = far + 1
    end
    return start > target and used or -1
end
local p = getplayerbyname("cover01")
sendmsg(p, 1, "最少广告牌 "
    .. cover({{1, 10}, {5, 20}, {20, 50}, {30, 60}}, 50))