I am learning about Big O Notation running times and amortized times. I understand the notion of O(n) linear time, meaning that the size of the input affects the growth of the algorithm proportionally…and the same goes for, for example, quadratic time O(n2) etc..even algorithms, such as permutation generators, with O(n!) times, that grow by … Read more
Yesterday I was pairing the socks from the clean laundry and figured out the way I was doing it is not very efficient. I was doing a naive search — picking one sock and “iterating” the pile in order to find its pair. This requires iterating over n/2 * n/4 = n2/8 socks on average. As … Read more
What is the most concise and efficient way to find out if a JavaScript array contains a value? This is the only way I know to do it: function contains(a, obj) { for (var i = 0; i < a.length; i++) { if (a[i] === obj) { return true; } } return false; } Is … Read more
I’d prefer as little formal definition as possible and simple mathematics. 4 43
Why does cache use Most Recently Used (MRU) algorithm as evict policy?
Example of O(n!)?
Using Commons Lang (to convert) + Collections (to min/max) import java.util.Arrays; import java.util.Collections; import org.apache.commons.lang.ArrayUtils; public class MinMaxValue { public static void main(String[] args) { char[] a = {‘3’, ‘5’, ‘1’, ‘4’, ‘2’}; List b = Arrays.asList(ArrayUtils.toObject(a)); System.out.println(Collections.min(b)); System.out.println(Collections.max(b)); } } Note that Arrays.asList() wraps the underlying array, so it should not be too memory intensive and … Read more
If the input matrix is guaranteed to describe transitive connectivity, it has a peculiar form that allows for an algorithm probing only a subset of the matrix elements. Here is an example implementation in Python: def count_connected_groups(adj): n = len(adj) nodes_to_check = set([i for i in range(n)]) # [] not needed in python 3 count = 0 … Read more
If you were using JGraph, you should give a try to JGraphT which is designed for algorithms. One of its features is visualization using the JGraph library. It’s still developed, but pretty stable. I analyzed the complexity of JGraphT algorithms some time ago. Some of them aren’t the quickest, but if you’re going to implement them on … Read more
public static void permutation(String str) { permutation(“”, str); } private static void permutation(String prefix, String str) { int n = str.length(); if (n == 0) System.out.println(prefix); else { for (int i = 0; i < n; i++) permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i+1, n)); } } (via Introduction to Programming in Java)
