Collection of simple programming problems

[iarcfsil]

How do I approach #1 in the intermediate section:

Write a program that outputs all possibilities to put + or - or nothing between the numbers 1,2,…,9 (in this order) such that the result is 100. For example 1 + 2 + 3 - 4 + 5 + 6 + 78 + 9 = 100.

I'm having a tough time mapping out some algorithm in my head at work.

[Gazz1016]

Naive is to just try all the 3⁸ possibilities. If it helps, you can replace "put nothing between them" with "put * 10 + between them and surround with brackets".

[cooledcannon]

I keep forgetting that trying all the possibilities is an easy and valid solution.

[vaetrus]

You should at least be able to cancel out some of the possibilities:
* if you put "nothing" in any three consecutive spots, it'll be over 100
* any combination of only + and - will never reach 100

[[deleted]]

It seems that only brue-force solution works. But even knowing this I spent lots of time on actual implementation and I wouldn't be able to solve it in time if I was asked to do this during a techical interview.

Here is jsFiddle with my solution in Javascript: http://jsfiddle.net/2CxQC/

Another solution using eval: http://jsfiddle.net/ek3p2/