DEV Community: Alexander Crescent

Answer: Essential skills of a Data Scientist [closed]

Alexander Crescent — Wed, 05 Feb 2020 02:22:46 +0000

answer re: Essential skills of a Data Scientist

May 19 '10

To quote from the intro to Hadley's phd thesis:

First, you get the data in a form that you can work with ... Second, you plot the data to get a feel for what is going on ... Third, you iterate between graphics and models to build a succinct…

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Answer: Essential skills of a Data Scientist [closed]

Alexander Crescent — Wed, 05 Feb 2020 02:22:29 +0000

answer re: Essential skills of a Data Scientist

Oct 15 '10

At dataist the question is addressed in a general way with a nice Venn diagram:

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Answer: Java Runtime Performance Vs Native C / C++ Code?

Alexander Crescent — Thu, 23 Jan 2020 18:17:31 +0000

answer re: Java Runtime Performance Vs Native C / C++ Code?

Dec 31 '09

Java isn't an interpreted language, and hasn't been for several versions. The Java bytecode is JIT'ed on the fly. (Technically it still interprets some of the code, but anything that matters performance-wise gets JIT'ed)

As for performance, what on Earth gives you the crazy idea that "there is a baseline…

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Answer: Spring boot app vs .war file deployed on Tomcat/Jetty [closed]

Alexander Crescent — Wed, 22 Jan 2020 14:54:21 +0000

answer re: Spring boot app vs .war file deployed on Tomcat/Jetty

Nov 17 '16

Package it to .war file and deploy it on Tomcat/Jetty?

Don't do this if at all possible. Reason: with embedded tomcat (or any other server runtime like undertow, netty, jetty etc) it's much easier to build a micro-services architecture.

As Josh Long once said in one of his Spring…

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Make Jar, not War.

Leetcode intersection of two linked lists

Alexander Crescent — Tue, 31 Dec 2019 08:16:46 +0000

https://leetcode.com/problems/intersection-of-two-linked-lists/discuss/49899/C++-solution-using-XOR-trick

Start from this:

   (p) a1 → a2
               ↘
                 X → c1 → c2
               ↗

(q) b1 → b2 → b3

follow p, reversing links as you go:

      a1 ← a2
              ↖
                X ← c1 ← c2 (p)
              ↗

(q) b1 → b2 → b3

now reverse q:

  (q) a1 → a2
              ↘
                X ← c1 ← c2 (p)
              ↙            
 b1 ← b2 ← b3

then reverse p again:

  (q) a1 → a2
              ↘
                X → c1 → c2
              ↗

(p) b1 → b2 → b3

Notice that p and q are swapped, but the list structure is back to what it was in the beginning.

Now the key observation: each node in branches a, b and c has been visited exactly twice, while X has been visited three times. We can thus use the well known trick: we keep an accumulator and XOR it to each address we visit along the way. In the end, the accumulator will contain the address of the only node visited an odd number of times, that is X.

What if the lists don't meet? In that case we have already reversed p twice, reverting it to its initial state, so we only need to reverse q a second time as well and return null.

Code

class Solution {
uintptr_t acc = 0;

ListNode* reverse(ListNode *head) {
    ListNode *prev = nullptr, *tmp;
    while (head) {
        acc ^= reinterpret_cast<uintptr_t> (head);
        tmp = head->next;
        head->next = prev;
        prev = head;
        head = tmp;
    }
    return prev;
}

public:
ListNode getIntersectionNode(ListNode *headA, ListNode *headB) {
ListNode *p = headA, *q = headB;
p = reverse(p);
q = reverse(q);
p = reverse(p);
if (q != headA) q = reverse(q);
return reinterpret_cast<ListNode> (acc);
}
};

Answer: What is uintptr_t data type

Alexander Crescent — Tue, 31 Dec 2019 08:14:05 +0000

answer re: What is uintptr_t data type

Dec 4 '09

203

uintptr_t is an unsigned integer type that is capable of storing a data pointer. Which typically means that it's the same size as a pointer.

It is optionally defined in C++11 and later standards.

A common reason to want an integer type that can hold an architecture's pointer type is…

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Answer: When should I write the keyword 'inline' for a function/method?

Alexander Crescent — Wed, 25 Dec 2019 23:46:50 +0000

answer re: When should I write the keyword 'inline' for a function/method?

Nov 18 '09

897

Oh man, one of my pet peeves.

inline is more like static or extern than a directive telling the compiler to inline your functions. extern, static, inline are linkage directives, used almost exclusively by the linker, not the compiler.

It is said that inline hints to the compiler…

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Answer: Advantages of using forward

Alexander Crescent — Wed, 25 Dec 2019 20:57:14 +0000

answer re: What are the main purposes of using std::forward and which problems it solves?

Aug 27 '10

800

You have to understand the forwarding problem. You can read the entire problem in detail, but I'll summarize.

Basically, given the expression E(a, b, ... , c), we want the expression f(a, b, ... , c) to be equivalent. In C++03, this is impossible. There are many attempts…

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Answer: What are rvalues, lvalues, xvalues, glvalues, and prvalues?

Alexander Crescent — Wed, 25 Dec 2019 20:44:52 +0000

answer re: What are rvalues, lvalues, xvalues, glvalues, and prvalues?

Mar 4 '12

165

Why are these new categories needed? Are the WG21 gods just trying to confuse us mere mortals?

I don't feel that the other answers (good though many of them are) really capture the answer to this particular question. Yes, these categories and such exist to allow move semantics, but the…

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Answer: When to use virtual destructors?

Alexander Crescent — Wed, 25 Dec 2019 17:30:20 +0000

answer re: When to use virtual destructors?

Apr 9 '13

223

A virtual constructor is not possible but virtual destructor is possible Let us experiment.......

#include <iostream>

using namespace std;

class Base
{
public:
    Base(){
        cout << "Base Constructor Called\n";
    }
    ~Base(){
        cout << "Base Destructor called\n";
    }
};

class Derived1: public Base
{
public:
    Derived1(){
        cout << "Derived constructor called\n";

…

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