# All Questions

**4312**

votes

**33**answers

572180 views

### What is a plain English explanation of "Big O" notation?

I'd prefer as little formal definition as possible and simple mathematics.

**1127**

votes

**16**answers

144420 views

### What is the best algorithm for an overridden System.Object.GetHashCode?

In .NET System.Object.GetHashCode method is used in a lot of places, throughout the .NET base class libraries. Especially when finding items in a collection fast or to determine equality. Is there a ...

**480**

votes

**64**answers

368636 views

### Algorithm to return all combinations of k elements from n

I want to write a function that takes an array of letters as an argument and a number of those letters to select.
Say you provide an array of 8 letters and want to select 3 letters from that. Then y...

**703**

votes

**49**answers

449058 views

### How to count the number of set bits in a 32-bit integer?

8 bits representing the number 7 look like this:
00000111
Three bits are set.
What are algorithms to determine the number of set bits in a 32-bit integer?

**409**

votes

**25**answers

283873 views

### What is the most effective way for float and double comparison?

What would be the most efficient way to compare two double or two float values?
Simply doing this is not correct:
bool CompareDoubles1 (double A, double B)
{
return A == B;
}
But something like...

**640**

votes

**33**answers

516600 views

### Calculate distance between two latitude-longitude points? (Haversine formula)

How do I calculate the distance between two points specified by latitude and longitude?
For clarification, I'd like the distance in kilometers; the points use the WGS84 system and I'd like to underst...

**443**

votes

**14**answers

89014 views

### What is the most efficient/elegant way to parse a flat table into a tree?

Assume you have a flat table that stores an ordered tree hierarchy:
Id Name ParentId Order
1 'Node 1' 0 10
2 'Node 1.1' 1 10
3 'Node 2' 0...

**738**

votes

**22**answers

341206 views

### Big O, how do you calculate/approximate it?

Most people with a degree in CS will certainly know what Big O stands for.
It helps us to measure how (in)efficient an algorithm really is and if you know in what category the problem you are trying t...

**380**

votes

**26**answers

382678 views

### How to generate all permutations of a list in Python

How do you generate all the permutations of a list in Python, independently of the type of elements in that list?
For example:
permutations([])
[]
permutations([1])
[1]
permutations([1, 2])
[1, 2]...

**608**

votes

**10**answers

413314 views

### How to find time complexity of an algorithm

The Question
How to find time complexity of an algorithm?
What have I done before posting a question on SO ?
I have gone through this, this and many other links
But no where I was able to find a c...