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请教一个math puzzle题

请教一个math puzzle题# JobHunting - 待字闺中

Q*82010-03-11 08:03

1 楼

请教大师们。。

m*i2010-03-11 08:03

2 楼

从careercup上看到的，不知道该怎么做，牛人指点一下
Given a cube. A ant is placed in a corner and cannot move. A spider starts
from the opposite corner, and can move along cube edges in any direction (x,
y,z) with probablity 1/3. What is the expected number of steps for this
spider to get to the ant?

F*t2010-03-11 08:03

3 楼

不是大师哈
是肉糜吗？可以包饺子，做京东肉饼，做meatball，做meatloaf，做chili

B*t2010-03-11 08:03

4 楼

This is an interview problem from quant, I don't think software developers
will be asked.
The answer is 10.
if you know Markov chain, it's quite easy. if not, a little bit harder.

x,

【在 m*******i 的大作中提到】

: 从careercup上看到的，不知道该怎么做，牛人指点一下
: Given a cube. A ant is placed in a corner and cannot move. A spider starts
: from the opposite corner, and can move along cube edges in any direction (x,
: y,z) with probablity 1/3. What is the expected number of steps for this
: spider to get to the ant?

Z*52010-03-11 08:03

5 楼

可以和豆芽什么的一起炒了，做盖浇饭

s*l2010-03-11 08:03

6 楼

http://www.mitbbs.com/article3/Quant/27138300_0_tn.html

【在 m*******i 的大作中提到】

m*h2010-03-11 08:03

7 楼

蚂蚁上树,炸酱面的肉酱

s*f2010-03-11 08:03

8 楼

假设spider在点A, ant在点D,

C---D
/| /|
B---C |
| B-|-C
|/ |/
A---B
那么另外6个点可以分成B和C两类:
然后我们来计算:
E(A) = E(B) + 1 //从A点怎么走都是到B点,所以是B点的expection + 1 step
E(B) = 1/3 (E(A)+1) + 2/3 (E(C)+1) //在B点有1/3可能性去A，2/3可能性去C
E(C) = 1/3 + 2/3 (E(B)+1) //在C点有1/3可能性就到了D，2/3的可能性去B
3个方程3个变量，解得E(A) = 10.

x,

【在 m*******i 的大作中提到】