Can you solve Dongle's Difficult Dilemma? - Dennis E. Shasha

2,261,685 views ・ 2021-04-26

TED-Ed


請雙擊下方英文字幕播放視頻。

譯者: Lilian Chiu 審譯者: Amanda Zhu
00:06
According to legend, when this planet was young and molten,
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根據傳說,
當這顆行星在很年輕的熔岩狀態時,
00:10
three galactic terraformers shaped it into a paradise.
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三位銀河地貌形塑師 將它塑造成天堂。
00:15
When their work was done, they sought out new worlds,
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他們完工之後,
就去尋找新世界了,
00:18
but left the source of their power behind:
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而留下了他們的力量來源:
00:21
three powerful golden hexagons,
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三個強大的六角黃金,
00:25
hidden within dungeons full of traps and monsters.
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藏在滿是陷阱和怪物的地牢中。
00:28
If one person were to bring all three hexagons together,
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如果有人能把三個六角黃金 通通集合在一起,
00:32
they could reinvent the world however they saw fit.
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就可以照自己的意思來重造世界。
00:36
That was thousands of years ago.
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這是數千年前的事。
00:39
Today, you’ve learned of Gordon, an evil wizard dead set on collecting the hexagons
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現在,你聽說邪惡的巫師高登
下定決定要找到這些六角黃金
00:45
and enslaving the world to his will.
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讓世界臣服在他腳下。
00:48
So you set off on a quest to get them first,
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於是你展開旅程,要搶先找到,
00:52
adventuring through fire, ice, and sand.
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冒險穿過烈火、冰天雪地、沙地。
00:56
Yet each time, you find that someone else got there first.
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但每一次你都發現有人捷足先登。
01:00
Not Gordon, but a merchant named Dongle.
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這個人不是高登, 而是名為丹戈的商人。
01:04
At the end of the third dungeon. you find a note inviting you to Dongle’s castle.
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在第三個地牢的盡頭, 你找到一張字條,
邀請你去丹戈的城堡。
01:09
You show up with a wallet bursting with the 99 gems
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你依邀請前往時,
皮夾裡裝滿了在旅途上 收集來的九十九顆寶石。
01:13
you’ve collected in your travels,
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01:14
arriving just moments before Gordon, who also has 99 gems.
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高登隨後來到,
同樣帶著九十九顆寶石。
01:20
Dongle has not only collected the golden hexagons,
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丹戈不僅收集到了所有六角黃金,
01:24
but he’s used them to create 5 silver hexagons,
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且已經用它們創造出了 五個六角白銀,
01:28
just as powerful as their golden counterparts.
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和六角黃金一樣強大。
01:31
Why did Dongle do all this?
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丹戈為什麼要這麼做?
01:33
Because there’s one thing he loves above all else: auctions.
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因為他對某件事的愛勝過一切:
拍賣。
01:38
You and the evil wizard will compete to win the hexagons,
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你要和邪惡巫師競爭以贏得六角金銀,
01:43
starting with the three golden ones,
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先從三個六角黃金開始,
01:45
making one bid for each item as it comes up.
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每個放出來時,可出價一次。
01:49
The winners of ties will alternate, starting with you.
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平手第一次算你贏,之後輪流。
01:53
Whoever first collects a trio of either golden or silver hexagons
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先收集到三個六角黃金 或三個六角白銀的人
01:58
can use their power to recreate the world.
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就可以用它們的力量去重建世界。
02:01
You’ve already bid 24 gems on the first,
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競標第一件物品時, 你已經用掉了二十四個寶石,
02:05
when you realize that your rival has a dastardly advantage:
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此時你才發現你的對手 有個很卑鄙的優勢:
02:09
a mirror that lets him see what you’re bidding.
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他有一面鏡子可以看到你的出價。
02:13
He bids zero, and you win the first hexagon outright.
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他出價零個寶石, 讓你贏得第一個六角黃金。
02:17
What’s your strategy to win a matching trio of hexagons before your rival?
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你要用什麼策略
才能比對手更早取得 三個黃金或三個白銀?
02:22
Pause here to figure it out for yourself.
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[自行解題,請在此暫停 答案公佈倒數:3]
02:24
Answer in 3
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02:25
Answer in 2
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[2]
02:27
Answer in 1
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[1]
02:31
Dongle’s dangled a difficult dilemma.
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丹戈製造了一個兩難的局面。
02:33
Do you spend big to try to win the golden hexagons outright?
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你會直接出高價取得六角黃金嗎?
02:37
Save as much as possible for silver? Or something in-between?
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還是盡可能保留給六角白銀?
或者折衷?
02:42
Gordon can use his magic mirror and 99 gems
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高登可以用他的魔法鏡子 以及九十九個寶石,
02:45
to make sure that no matter what you bid on the second gold,
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不論你對第二個六角黃金出價多少,
02:49
he can bid one more and block you.
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他都能多出價一個寶石來阻止你。
02:51
So the real question is— how can you force Gordon to spend enough on the golds
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所以真正的問題是——
你要如何迫使高登 在六角黃金上花費夠多寶石,
02:57
to guarantee that you’ll win on the silvers?
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以確保你能贏得三個六角白銀?
03:01
Here’s a hint.
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提示如下。
03:02
Let’s say at the start of the silver auctions
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假設在六角白銀拍賣開始時,
03:05
you had a one gem advantage, such as 9 to 8.
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你有多一顆寶石的優勢,
比如九比八。
03:09
You need to win three auctions,
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你得贏三場拍賣,
03:12
so could you divide your gems into three groups of three and win?
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所以,你可以把你的寶石 三個三個分為一組並獲勝?
03:17
For simplicity, let’s assume a set of rules that’s worse for you,
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為了簡化問題,
咱們就假設你們用的是 一組對你不利的規則,
03:21
where Gordon wins every tie.
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也就是每次平手都是高登贏。
03:24
If you bid 3 each time, the best he could do
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如果你每次出價三顆寶石,
對他來說最好的狀況 就是贏得兩個六角白銀
03:27
is win two silver hexagons, and have two gems left—
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並剩下兩顆寶石——
03:31
which you’ll beat with three bids of 3.
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你後面三次都出價三顆寶石就贏了。
03:34
Any one-gem advantage where your starting total is divisible by three
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只要開始時你的寶石 總數比對方多一個
且可以被三整除,
03:39
will lead to victory by the same logic.
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都能依同樣的邏輯讓你獲勝。
03:43
So knowing that, how can you force Gordon's hand in the gold auctions
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知道這一點之後,
你要如何迫使高登依你的意思 投入六角黃金的拍賣,
03:47
so you go into silver with an advantage?
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讓你在六角白銀的拍賣上能佔優勢?
03:50
Let’s first imagine that Gordon lets you win the second gold auction
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先想像一下,如果高登 跟你一樣出價 x 顆寶石,形成平手,
03:54
by betting some amount X with a tie.
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讓你贏了第二件六角黃金。
03:58
You could then bid everything you have left on the third gold hexagon,
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你就可以把你剩下的一切 都押在第三個六角黃金上,
04:02
and he'd have to match you to block.
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他得出同價才能阻止你。
04:05
So if you could bid 51 on the third gold,
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所以,如果你能出價五十一顆 寶石買第三個六角黃金,
04:08
you'd go into silver with a 51 to 48 advantage, which you know you can win.
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進入六角白銀的拍賣時, 你就有五十一比四十八的優勢,
你知道這樣你就贏定了。
04:15
Solving for X reveals that in order to have 51 on round three,
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未知數 X 的解法:
為了在第三輪時擁有五十一顆寶石,
04:20
you should bid at most 24 on round two.
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在第二輪你最高只能 出價二十四顆寶石。
04:24
But what about the other possibility,
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但另一種可能性呢?
04:27
where Gordon wins the second gold against your bid of 24—
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如果你出價二十四顆寶石,高登出價 更高取得了第二個六角黃金,
04:31
would this strategy still work?
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這項策略還行得通嗎?
04:34
The least he could bid to win the second gold is 25,
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要取得第二個六角黃金, 他最少要出二十五顆寶石,
04:38
making the total 75 to Gordon’s 74.
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這樣你共有七十五顆寶石, 高登只有七十四顆。
04:42
No one would then bid on round three,
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第三輪就沒有人會出價,
04:45
since you’ve each blocked the other from getting three golds.
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因為你們都已經成功阻止對方 取得三個六角黃金了。
04:49
After that, you could bid 25 every time to win three silvers.
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接下來,你可以 每次出價二十五顆寶石,
贏得三個六角白銀。
04:55
The bidding war was close,
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拍賣戰爭即將開始,但你的足智多謀
04:56
but your ingenuity kept you one link ahead in the chain of inference,
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讓你能在推論鏈上領先一環,
05:01
and the silver tri-source is yours.
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三個六角白銀的力量來源 就歸你所有了。
05:04
Now... what will you do with it?
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那現在……你要拿它來做什麼?
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