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Fast permutation -> number -> permutation mapping algorithms
...you have n possibilities, so you can describe this with a number between 0 and n-1. For the position that the next element ends up at, you have n-1 remaining possibilities, so you can describe this with a number between 0 and n-2.
Et cetera until you have n numbers.
As an example for n = 5, consid...
Most efficient way to store thousand telephone numbers
...digits left. We view these remaining five digits as 17-bit binary integers and store k of those bits using one method and 17 - k = m with a different method, determining k at the end to minimize the required space.
We first sort the phone numbers (all reduced to 5 decimal digits). Then we count how...
How to replace a hash key with another key
...akes some time to tell what it is really doing. Your solution is in other hand simple and descriptive.
– Lucas
Nov 13 '14 at 18:55
3
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Remove blank attributes from an Object in Javascript
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Hi, @EricNguyen, unlike C and other several languages, javascript does not have block scope for variables (only function scope), thus, the variable i will always leak into the scope after the for block.
– Gerardo Lima
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The $.param( ) inverse function in JavaScript / jQuery
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You should use jQuery BBQ's deparam function. It's well-tested and documented.
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How to merge dictionaries of dictionaries?
...for key in b:
if key in a:
if isinstance(a[key], dict) and isinstance(b[key], dict):
merge(a[key], b[key], path + [str(key)])
elif a[key] == b[key]:
pass # same leaf value
else:
raise Exception('Conflict at %...
How to find the kth largest element in an unsorted array of length n in O(n)?
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This is called finding the k-th order statistic. There's a very simple randomized algorithm (called quickselect) taking O(n) average time, O(n^2) worst case time, and a pretty complicated non-randomized algorithm (called introselect) taking O(n) worst case time. There's some info on Wikipedia, bu...
Easy interview question got harder: given numbers 1..100, find the missing number(s) given exactly k
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Here's a summary of Dimitris Andreou's link.
Remember sum of i-th powers, where i=1,2,..,k. This reduces the problem to solving the system of equations
a1 + a2 + ... + ak = b1
a12 + a22 + ... + ak2 = b2
...
a1k + a2k + ... + akk = bk
Using Newton's...
Efficient way to remove keys with empty strings from a dict
I have a dict and would like to remove all the keys for which there are empty value strings.
17 Answers
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Update value of a nested dictionary of varying depth
...ight general idea, i.e. a recursive solution, but somewhat peculiar coding and at least one bug. I'd recommend, instead:
Python 2:
import collections
def update(d, u):
for k, v in u.iteritems():
if isinstance(v, collections.Mapping):
d[k] = update(d.get(k, {}), v)
...