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One interview question

One interview question# JobHunting - 待字闺中

w*f2012-05-18 07:05

1 楼

5 'A'
4 'B'
3 'C'
Q: how many unique 5-letter words can be formed?
It took me long time to thinks, but interviewer didn't happy with my
final answer.
If all 5 'A', 'B', 'C', the combination is 3^5 = 243;
missing 5'B', 1
missing 5'C', 1
missing (A/B) 4C, 10
total is 3^5 -1 -1 -10 = 231;
do I get it right (after interview)?

d*u2012-05-18 07:05

2 楼

5 4 3 是神马？5个a？

s*r2012-05-18 07:05

3 楼

我认为楼主的答案是对的。

【在 w****f 的大作中提到】

: 5 'A'
: 4 'B'
: 3 'C'
: Q: how many unique 5-letter words can be formed?
: It took me long time to thinks, but interviewer didn't happy with my
: final answer.
: If all 5 'A', 'B', 'C', the combination is 3^5 = 243;
: missing 5'B', 1
: missing 5'C', 1
: missing (A/B) 4C, 10

w*f2012-05-18 07:05

4 楼

可惜在最后，
我只是给出了 3^5 - 1 -1 -10
没有给出答案是 231

【在 w****f 的大作中提到】

w*f2012-05-18 07:05

5 楼

What is general formula for this unique letter?
Numerical try: 12! / (5!*4!*3!)/5! =231 , 数字巧合？还是有规律？
Total permutation is 12!
duplicate : 5! * 4! * 3!
then what about last 5! ?

Another try: 12!/7! / (5!*4!*3!)/5! =5.5 failed.

l*82012-05-18 07:05

6 楼

巧合吧

【在 w****f 的大作中提到】

: What is general formula for this unique letter?
: Numerical try: 12! / (5!*4!*3!)/5! =231 , 数字巧合？还是有规律？
: Total permutation is 12!
: duplicate : 5! * 4! * 3!
: then what about last 5! ?
:
: Another try: 12!/7! / (5!*4!*3!)/5! =5.5 failed.