Interview Question - Mergesort in C#

public List<int> MergeSort(List<int> m) {
if (m.Count() <= 1) return m;
int mid = m.Count() / 2;
List<int> left = new List<int>(), right = new List<int>();

for (int i = 0; i < mid; i++) left.Add(m[i]);
for (int i = mid; i < m.Count(); i++) right.Add(m[i]);

left = MergeSort(left);
right = MergeSort(right);
return Merge(left, right);
}

public List<int> Merge(List<int> a, List<int> b) {
int aCount = 0, bCount = 0;
List<int> m = new List<int>();

while (m.Count() < a.Count() + b.Count()) {
if (aCount < a.Count() && bCount < b.Count())
m.Add(a[aCount] < b[bCount] ? a[aCount++] : b[bCount++]);
else
m.Add(aCount < a.Count() ? a[aCount++] : b[bCount++]);
}

return m;
}

I realize that nowadays when I practice interview questions I'm tending less towards readability and convention (using var for local variables in C#) in favor of less lines of code (using var means you have to declare each variable on a separate line of code) - when doing interview practice you just wanna get the answer on the page and move on.  I could have refactored the while loop in my Merge function into many more lines of code but opted for the a cryptic version instead, which makes me feel like a boss but may be more confusing to readers the first time through.  So I apologize for that

Interview Question - Write an algorithm to determine if n is a power of 2

If I have the idea correctly, you can actually do this in constant time.

First piece of useful information: Any power of 2 is represented in memory as 0...010...0

Examples:
2 is 00000010
4 is 00000100
8 is 00001000
16 is 00010000

Second piece of useful information: x & (x - 1) is a neat little hack that will return x with its least significant bit cleared out.
What does that do for the examples above?  Just makes them all 0!

So here's the code I wrote:

bool IsPowerOf2(int x) {
   return x > 0 && (x & (x - 1)) == 0;
}

///Update: Crap. This was on stackoverflow already.  Oh well

Good News :)

After months and months of studying, interviewing, and (mostly) getting rejected from many, various, companies, I finally feel like all of this was worth it.

I just accepted an offer from Microsoft, although I also passed my Google interviews and would be in "Google limbo" where I would get matched up with a potential future team.  Getting this close to a Google offer is certainly very enticing, but I'm really drawn to the Microsoft Explore program where I would get to experience all three roles of software (development, testing, and program management).  It's a program that I haven't seen implemented in other companies and it's a once-in-a-lifetime opportunity; after this year I would no longer be eligible for it.

I can't even put into words how good it finally feels to have an (awesome!!) internship in tow for the summer.  After averaging 3 interviews a week for about two months, stressing out before hand, ditching class in the hope that an extra few hours of studying would pay off during interviews, or thinking about this summer and not having a place to call home - it's finally all done and I have an offer I am so very proud of, in my favorite city in this country.  So often I have imagined myself living in Seattle among all of the other tech geeks, now it's finally going to happen.

This post has no benefit to anyone else, just me.  It's my self-congratulatory message to myself.  After months and months of difficulty I feel like I am allowed to pat myself on the back, just this once.  Thanks to my family, friends, and friendly Microsoft recruiters for their support :)