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Closed 10 years ago.
I came across this question and couldn't figure out how to approach it. Can someone please help me out? The question is-
Add numbers in base n (not any of the popular ones like 10, 16, 8 or 2 - I hear that Charles Simonyi, the inventor of Hungarian Notation, favors -2 when asking this question).
I just need the idea.
You didn't specify a language, but you could just convert the base n number into a standard integer and add it.
Suppose base N number = '...d2d1d0' where di = the i'th digit.
Number = ... d2 * N^2 + d1 * N^1 + d0 * N^0
Then just add the numbers as usual.
Idea: it looks like hashing, but in hash function you can't use negative numbers.
Related
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Closed 10 years ago.
I have N points. Each point has X and Y coordinates.
I need to find X and Y of center of mass this points. Can you give me an algorithm to accomplish this task?
Is there something wrong with just taking the weighted average by mass?
for each point n
{
totalmass += n.mass
totalx += n.x*n.mass
totaly += n.y*n.mass
}
center = (totalx/totalmass,totaly/totalmass)
add additional dimensions as appropriate.
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Closed 11 years ago.
Please help solve this:
Telephone numbers are often given out as a word representation, so that they are easy to remember. For example if my number is 4357, the text given is HELP. There could be many other possibilities with the same digits, most of which do not make sense.
Write a space-and-time-optimal function that can, given a phone number, print the possible words that can be formed from it.
Based on the detailed explanation in the comment this should be a simple permutation combination problem:
Each digit will have a number of characters associated to it (example 4 could mean either of G,H or I) and then for a combination of digits the permutation can be computed.
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Closed 11 years ago.
There is a 3D grid with cells for which we define its value (0 or 1) as F(i,j,k)=F(i-1,j,k) XOR F(i,j-1,k) XOR F(i,j,k-1), base cases are F(0,0,0)=1 and F(x,y,z)=0 for x < 0 or y < 0 or z < 0 (if at least one parameter is negative).
We want to count amount of cells with F()=1 in the cube with corners (0,0,0) and (N, M, K). Dimensions are about 2^30.
I'm looking for the fast approach on this problem.
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Closed 11 years ago.
Say you wanted to find which input causes function x to output value y, and you know the (finite) range of possible inputs.
The input and output are both numbers, and positively correlated.
What would be the best way to optimize that?
I'm currently just looping through all of the possible inputs.
Thanks.
One solution would be a binary search over the possible inputs.
Flow:
find the median input x
get the output from function(x)
if the output is less than the desired y
start over using the smaller half of the possible inputs
else
start over using the larger half of the possible inputs
A binary search algorithm, perhaps?
http://en.wikipedia.org/wiki/Binary_search_algorithm
If the range is finite and small, a precomputed lookup table might be the fastest way
if you have some sets of know "x" data that yield "y" you can divied between training and test sets and use neural networks.
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Closed 11 years ago.
Problem statement:
You are given a set of k strings, each length n. You have to output the group of anagrams together. Anagrams are like e.g atm - mat , like-kile.
Just sort the word's letters to obtain a signature that's anagram-specific. E.g., in Python,
sig = ''.join(sorted(word))
and make a dict with sig as the key and the value being a list of words with that signature (defaultdict(list) works well for this). Of course, you can do it in any language with sorting abilities, and associative arrays whose values can be lists or vectors;-).