1. ## Challenge

Code:
```
8809 = 6    9881 = 5
7111 = 0    7756 = 1
2172 = 0    5555 = 0
6666 = 4    8193 = 3
1111 = 0    8096 = 5
3213 = 0    1012 = 1
7662 = 2    7777 = 0
9313 = 1    9999 = 4
0000 = 4    5531 = 0
2222 = 0    6855 = 3
3333 = 0    2581 = ?
```
 This problem can be solved by pre-school children in 5-10 minutes, by programmers in an hour and by people with higher education… well, check it yourself!  Reply With Quote

2. Interesting puzzle.
 I have worked out its addition by substitution i.e. 0 = 1, 1 = 0, 2 = 0, 3 = 0, 4 = ?, 5 = 0, 6 = 1, 7 = 0, 8 = 2, 9 = 1  Reply With Quote

 2  Reply With Quote

4. well, I would never solved it, but Google as usual is my friend...  Reply With Quote

5. i also googled for solution   Reply With Quote

6. This is kind of neat. I posted this from a discussion about creative thinking, how we need to discard old patterns and pre-conceived notions. Something I'm sure everyone realizes is at times useful to reversing. From the posts so far I see at least 3 different strategies to how you solved it (including google), and one I never considered. Here's the article:

http://codejury.com/what-genius-really-means/

I suspect there may even be "harder" and more complex ways to solve this. Captcha? Pattern recognition?  Reply With Quote

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