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过河谜题

Can you solve the river crossing riddle? - Lisa Winer

野火席卷了整个草原
As a wildfire rages throughthe grasslands,
3头狮子和3只羚羊逃命出来
three lions and three wildebeestflee for their lives.
为了逃离地狱
To escape the inferno,
它们必须越过满布鳄鱼的小河 到达左岸 幸运的是
they must cross over to the left bank of a crocodile-infested river. Fortunately,
附近有个竹筏
there happensto be a raft nearby.
一次能装载两个动物
It can carry up to two animals at a time,
同时 需要至少一个动物在船上
and needs as least one lionor wildebeest on board
这样竹筏才能动
to row it across the river.
有一个问题
There’s just one problem.
如果河岸上狮子数目超过羚羊
If the lions ever outnumber the wildebeest
不管是哪个河岸
on either side of the river,
即使一瞬 它们的本能会爆发
even for a moment, their instincts will kick in,
结果很糟糕
and the results won’t be pretty.
船上的动物到岸上的情况
That includes the animals in the boat when it’s
也包含在内
on a given side of the river.
如果狮子不大开杀戒 那么
What’s the fastest way for all six animalsto get across
这6只动物怎样最快渡河?
without the lions stopping for dinner?
如果你想自己解开这个问题 请暂停
Pause here if you wantto figure it out for yourself.
答案揭晓倒计时 3 2 1
Answer in: 3 Answer in: 2 Answer in: 1
如果你被这样的问题困住了
If you feel stuck on a problem like this,
试试列举出每个你能做出的决定
try listing all the decisions you can makeat each point,
以及每个选择导致的结果
and the consequences each choiceleads to.
比如 第一次谁坐船 有5种选择:
For instance, there are five optionsfor who goes across first:
1只羚羊 1头狮子 两只羚羊
one wildebeest, one lion, two wildebeest,
两头狮子 或是各有一个
two lions, or one of each.
如果只有一个动物过河 那它得直接回来
If one animal goes alone, it’ll just have to come straight back.
如果两只羚羊先走 剩下的一只马上会被吃掉
And if two wildebeest cross first, the remaining one will immediately get eaten.
所以 那些选项被剔除出去
So those options are all out.
两头狮子先走 或是 各有一个动物先走
Sending two lions, or one of each animal,
都可以推出解决方案 且所花步骤一样
can actually both lead to solutions in the same number of moves.
为了节约时间 我们关注第二个方案
For the sake of time,we’ll focus on the second one.
各有一个动物渡河 现在
One of each animal crosses. Now,
如果羚羊留下 狮子回去
if the wildebeest staysand the lion returns,
右岸上就有3个狮子了
there will be three lionson the right bank.
这对于剩下的两个羚羊来说是个坏消息
Bad news for the two remaining wildebeest.
所以我们需要让狮子留在左岸
So we need to have the lion stay on the left bank
羚羊回到右岸
and the wildebeest go back to the right.
现在我们又有相同的5种选择
Now we have the same five options,
但是左岸已经有一头狮子了
but with one lionalready on the left bank.
如果两只羚羊离开 那么留下的那个会被吃
If two wildebeest go,the one that stays will get eaten,
如果各一个动物离开
and if one of each animal goes,
一旦竹筏到达对岸
the wildebeest on the raftwill be outnumbered
竹筏上的羚羊数量最少
as soon as it reaches the other side.
所以行不通 这意味着 第三次渡河
So that’s a dead end, which means that at the third crossing,
只有两个狮子可以离开
only the two lions can go.
一只上岸 左岸上留下两头狮子
One gets dropped off, leaving two lions on the left bank.
第三头狮子划船去到右岸
The third lion takes the raft back tothe right bank
在那儿 羚羊正等着
where the wildebeest are waiting.
现在该如何呢?
What now? Well,
因为左岸上有两头狮子在等
since we’ve got two lions waitingon the left bank,
唯一的选项是让两只羚羊渡河 接下来
the only option is for two wildebeestto cross. Next,
再让两只羚羊回去是无意义的
there’s no sense in two wildebeestgoing back,
因为这是上一步的逆向行为
since that just reverses the last step.
如果两头狮子回去
And if two lions go back,
那么右岸上的狮子数量会多于羚羊
they’ll outnumber the wildebeest on the right bank.
所以只能是一头狮子和一只羚羊划船回去
So one lion and one wildebeesttake the raft back
这样 左岸各有一只动物
leaving us with one of each animalon the left bank
右岸各有两个动物 同样地
and two of each on the right. Again,
再派一只狮子和一只羚羊组合回去是无意义的
there’s no point in sendingthe lion-wildebeest pair back,
所以 下一次旅行应该要不就是两头狮子
so the next trip should be eithera pair of lions
要不就是两只羚羊
or a pair of wildebeest.
如果狮子离去
If the lions go,
在左岸 狮子会吃羚羊 所以它们要留下来
they’d eat the wildebeest on the left, so they stay,
两只羚羊渡河
and the two wildebeest cross instead.
现在 我们马上就要解开问题了
Now we’re quite close
因为羚羊已经达到目的地了
because the wildebeest are all where they need to be
数量上看 就安全了
with safety in numbers.
剩下的就是 让一头狮子划船回去
All that’s left is for that one lionto raft back
一个一个把它的同伙接过来
and bring his fellow lions overone by one.
总共是11趟
That makes eleven trips total,
是让每只动物安全到达对岸的最少趟数
the smallest number neededto get everyone across safely.
如果先派两头狮子渡河的方法
The solution that involves sending both lions
与此相似
on the first step works similarly,
也需要11步
and also takes eleven crossings.
这6个动物安全无恙地及时逃离出来
The six animals escape unharmedfrom the fire just in time
过了河 开始了它们新的生活
and begin their new livesacross the river.
当然 现在危险已经渡过
Of course, now that the danger’s passed,
它们之间不太可能的联盟不知能持续多久呢
it remains to be seen how long their unlikely alliance will last.

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视频概述

严谨的逻辑 一步步推导 得出最终结论

听录译者

收集自网络

翻译译者

lala

审核员

审核员 V

视频来源

https://www.youtube.com/watch?v=ADR7dUoVh_c

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