Google campus interview

1. Design a web application system. What you need to take care
Guess:   Scalability/ loading balancer, security, robust(network failure /disconnection), database atomicity, compatibility

2. Write a function do print all combination of a string like "ABC" -> {"ABC", "ACB", "BAC",...}
look PIE

3. Write a function computes the mirror of a 1-bit image array (each pixel is one bit). The mirror is an output image which is right-side-left to its central axis.
I die in this question.
At least you need to mention what will happen when byte is not align.
Guess: create helper function:
ReverseBits( int start_bit_offset, int end_bit_offset) and use it on every row.