Fun Programming Quizzes

noAxioms

I know. I was admiring it.
I think it can be done with no loops at all.

Efram

I think it can be done with no loops at all. — noAxioms

Challenge accepted.

noAxioms

Don't think you'll keep it to 60 lines. Is multiple calls to isPrime(x) function cheating?

Side note: The language requires the empty else { } clauses? Not used to that as a C person.
I have a harder time thinking in C anymore since I'm pure C++ now.

Efram

That's just my failure to clean up after myself; there used to be code in those blocks.

_db

Hey can someone please do my programming assignment for me

_db

I'll pay you

SophistiCat

Is there really a way to know the number of primes below any integer without having to actually calculate or iterate through those primes? — VagabondSpectre

Prime-counting function

Jamal

Btw for the web developers among you, which text editor do you use? Atom, Coda, Sublime, Textastic, Brackets or something else? — Agustino

I used Sublime for a long time, but now I use Visual Studio Code. There's not a huge difference, but it seems more solid, and looks prettier with less fiddling around.

SophistiCat

↪andrewk

Or, you know, you could just calculate the answer :)

The sum of multiples of 3 below 1000:

3 + 6 + 9 + ... + 999 = 3 * (1 + 2 + 3 + ... + 333) = 3 * 333 * 334 / 2

Likewise, the sum of multiples of 5 below 1000 is 5 * 199 * 200 / 2

But we also need to subtract the sum of multiples of 15, since we counted them in both sums: - 15 * 66 * 67 / 2

Total: 233,168

Agustino

↪VagabondSpectre

Yeah, that seems to work. Here was mine:

public int makeChocolate(int small, int big, int goal) {
  if( small+5*big>=goal && goal%5<=small){
    if (5*big < goal) {
    return goal-5*big;
    }
    return goal%5;
  } else {
    return -1;
  }
}

Though I will say that one of your conditions is redundant (below is the shorter version with that condition removed):

public int makeChocolate(int small, int big, int goal) {
  int remainder = goal%5;

  if (goal > big*5+small || remainder > small) { 
    return -1;
  }
  if (big*5 < goal) {   
    return goal-big*5;
  }
  return remainder;
}

Agustino

Hey can someone please do my programming assignment for me — darthbarracuda

That depends on (1) what is your programming assignment, (2) what programming language are we talking about, (3) how much are you paying? and (4) if that person is fine with the ethics of the situation. But in short - we need more details.

Quite often I see people asking for something generally like that, and it's not helpful to anyone - I don't even know if I can help you based on the info you have provided for example.

I'll pay you — darthbarracuda

And another important question is how are you paying... because Paypal payments aren't very secure, there is no seller protection for digital goods (but there is buyers' protection though - very messed up). Many programmers aren't even aware of this lol.

Hire a programmer, get the work done, and then go to your bank and file a chargeback aimed at Paypal :P - that's what a ruthless businessman would do >:O

So programmers need to be careful with Paypal as a payment option.

Agustino

https://projecteuler.net/problem=67

So I was trying to solve that last night. I had solved the previous one which involved a smaller triangle awhile ago through an evolutionary algorithm - see below (all are written and run in the Processing java-based language).

The evolutionary algorithm works by making a "first guess" at the solution, which is a greedy algorithm, which chooses the best path to take down the triangle at each juncture, without any looking into the future. It records this path as 0s and 1s, with 0 = take a left, and 1 = take a right. Then it takes this first guess at a path, creates copies of it, mutates them (with certain probabilities), and then tests which one from that generation is the best. It selects it, and returns to the beginning by re-creating copies of it, modifying them, testing, etc.

String triangle = "59 73 41 52 40 09 26 53 06 34 10 51 87 86 81 61 95 66 57 25 68 90 81 80 38 92 67 73 30 28 51 76 81 18 75 44 84 14 95 87 62 81 17 78 58 21 46 71 58 02 79 62 39 31 09 56 34 35 53 78 31 81 18 90 93 15 78 53 04 21 84 93 32 13 97 11 37 51 45 03 81 79 05 18 78 86 13 30 63 99 95 39 87 96 28 03 38 42 17 82 87 58 07 22 57 06 17 51 17 07 93 09 07 75 97 95 78 87 08 53 67 66 59 60 88 99 94 65 55 77 55 34 27 53 78 28 76 40 41 04 87 16 09 42 75 69 23 97 30 60 10 79 87 12 10 44 26 21 36 32 84 98 60 13 12 36 16 63 31 91 35 70 39 06 05 55 27 38 48 28 22 34 35 62 62 15 14 94 89 86 66 56 68 84 96 21 34 34 34 81 62 40 65 54 62 05 98 03 02 60 38 89 46 37 99 54 34 53 36 14 70 26 02 90 45 13 31 61 83 73 47 36 10 63 96 60 49 41 05 37 42 14 58 84 93 96 17 09 43 05 43 06 59 66 57 87 57 61 28 37 51 84 73 79 15 39 95 88 87 43 39 11 86 77 74 18 54 42 05 79 30 49 99 73 46 37 50 02 45 09 54 52 27 95 27 65 19 45 26 45 71 39 17 78 76 29 52 90 18 99 78 19 35 62 71 19 23 65 93 85 49 33 75 09 02 33 24 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60 85 59 39 60 07 57 76 77 92 06 35 15 72 23 41 45 52 95 18 64 79 86 53 56 31 69 11 91 31 84 50 44 82 22 81 41 40 30 42 30 91 48 94 74 76 64 58 74 25 96 57 14 19 03 99 28 83 15 75 99 01 89 85 79 50 03 95 32 67 44 08 07 41 62 64 29 20 14 76 26 55 48 71 69 66 19 72 44 25 14 01 48 74 12 98 07 64 66 84 24 18 16 27 48 20 14 47 69 30 86 48 40 23 16 61 21 51 50 26 47 35 33 91 28 78 64 43 68 04 79 51 08 19 60 52 95 06 68 46 86 35 97 27 58 04 65 30 58 99 12 12 75 91 39 50 31 42 64 70 04 46 07 98 73 98 93 37 89 77 91 64 71 64 65 66 21 78 62 81 74 42 20 83 70 73 95 78 45 92 27 34 53 71 15 30 11 85 31 34 71 13 48 05 14 44 03 19 67 23 73 19 57 06 90 94 72 57 69 81 62 59 68 88 57 55 69 49 13 07 87 97 80 89 05 71 05 05 26 38 40 16 62 45 99 18 38 98 24 21 26 62 74 69 04 85 57 77 35 58 67 91 79 79 57 86 28 66 34 72 51 76 78 36 95 63 90 08 78 47 63 45 31 22 70 52 48 79 94 15 77 61 67 68 23 33 44 81 80 92 93 75 94 88 23 61 39 76 22 03 28 94 32 06 49 65 41 34 18 23 08 47 62 60 03 63 33 13 80 52 31 54 73 43 70 26 16 69 57 87 83 31 03 93 70 81 47 95 77 44 29 68 39 51 56 59 63 07 25 70 07 77 43 53 64 03 94 42 95 39 18 01 66 21 16 97 20 50 90 16 70 10 95 69 29 06 25 61 41 26 15 59 63 35";
String triangle2 = "75 95 64 17 47 82 18 35 87 10 20 04 82 47 65 19 01 23 75 03 34 88 02 77 73 07 63 67 99 65 04 28 06 16 70 92 41 41 26 56 83 40 80 70 33 41 48 72 33 47 32 37 16 94 29 53 71 44 65 25 43 91 52 97 51 14 70 11 33 28 77 73 17 78 39 68 17 57 91 71 52 38 17 14 91 43 58 50 27 29 48 63 66 04 68 89 53 67 30 73 16 69 87 40 31 04 62 98 27 23 09 70 98 73 93 38 53 60 04 23";
// triangle = active one, problem 67 now. triangle2 = inactive one, problem 18.
String[] total = split(triangle, " ");
int size = 200;
int probability_switch = 200; // reads 1 out of 200
int probability_scramble = 15; // 1 out of 15
int probability_inversion = 100; // 1 out of 100

int[] path_genome(int[] nums) {
  int rows = (-1+int(sqrt(1+8*total.length)))/2;;
  int[] moves = new int[rows];
  int pos = 0;
  for(int i=1; i<=rows; i++) {
    if(i<rows) {
    if(nums[i+pos]>nums[i+pos+1]) {
      pos += i;
      moves[i] = 0;
    } else {
      pos += i+1;
      moves[i] = 1;
    }
    }
  }
  return moves;
}

int getFitness(int[] path, int[]triangles) {
  int pos = 0;
  int fitness = triangles[pos];
  for(int i=1; i<path.length; i++) {
    pos += i+path[i];
    fitness += triangles[pos];
  }
  return fitness;
}

int[] doMutation(int[] path) {
  //FLIP Mutation
  for (int i = 1; i < path.length; i++) {
     if(floor(random(probability_switch))==1){
       if(path[i]==1) {
        path[i] = 0; 
       } else {
         path[i] = 1;
       }
     }
     
      //SCRAMBLE MUTATION
   if(floor(random(probability_scramble))==1) {
   int start_position = floor(random(path.length));
   int end_position = floor(random(path.length));
   if (start_position > end_position) {
    int temp = start_position;
    start_position = end_position;
    end_position = temp;
   }
   for (i = start_position; i < end_position; i++) {
     int pick = floor(random(start_position, end_position+1));
     int temp = path[i];
     path[i] = path[pick];
     path[pick] = temp;
     }
   }
   
   //INVERSION MUTATION
   if(floor(random(probability_inversion))==1) {
   int start_position = floor(random(path.length));
   int end_position = floor(random(path.length));
   if (start_position > end_position) {
    int temp = start_position;
    start_position = end_position;
    end_position = temp;
   }
   int n =0;
   for (i = start_position; i < ceil((end_position+start_position)/2); i++) {
     int pick = end_position-n;
     int temp = path[i];
     path[i] = path[pick];
     path[pick] = temp;
     n++;
     }
   }
   }
   return path;
}

int[][] getGenePool(int[] path) {
  int[][] pool = new int[size][path.length];
  for (int i=0; i<size; i++) {
    pool[i] = makeArrayCopy(path);
  }
  return pool;
}

int[] makeArrayCopy(int[] old) {
  int[] copy = new int[old.length];
  for(int i = 0; i<old.length; i++){
        copy[i] = old[i];
    }
    return copy;
}

int getFittest(int[][] pool, int[] nums) {
  int fittest_loc = 0;
  int fitness_new = 0;
  int fitness = 0;
  for(int i=0; i<size; i++) {
    fitness_new = getFitness(pool[i], nums);
    if(fitness_new > fitness) {
      fitness = fitness_new;
      fittest_loc = i;
    }
  }
  return fittest_loc;
}

void setup() {
  int[] nums = int(split(triangle, " "));
  int[] path = path_genome(nums);
  int fitness_loc = 0;
  int numGens = 0;
  while(numGens<1000000) {
  numGens++;
  int[][] pool = getGenePool(path);
  for(int i=1; i<size; i++) {
    pool[i]=doMutation(pool[i]);
  }
  fitness_loc = getFittest(pool, nums);
  path = pool[fitness_loc];
  if(numGens%5000==0) {
    println(getFitness(path, nums));
  }
  }
  println(getFitness(path, nums));
}

Now, this evolutionary algorithm doesn't manage to solve Problem 67 (although I expected it to, that's why I chose to use it for the first problem, instead of trying brute force), though it gets very close to the answer - gets to around ~7200 and the answer is 7273.

Here's a dynamic programming way to solve it, also written in Processing. Basically, it solves each "small" triangle starting at the very bottom, and then records that answer on the row above.

Note - to run this one, you must download the .txt file from the first link and then save it in the same folder as the program.

void setup() {
  int[][] triangle = readInput("triangle.txt");
  int lines = triangle.length;
  for(int i = lines-2; i>=0; i--) {
   for(int j = 0; j < i+1; j++) {
     if(triangle[i+1][j]>triangle[i+1][j+1]) {
       triangle[i][j] += triangle[i+1][j];
     } else {
     triangle[i][j] += triangle[i+1][j+1];
     }
   }
  }
  println(triangle[0][0]);
}

int[][] readInput(String filename) {
  String line;
  String[] linePieces;
  int lines = 0;
  BufferedReader reader;
  BufferedReader reader2;
  reader = createReader(filename);
  reader2 = createReader(filename);
  
  try {
    while ((line = reader.readLine()) != null) {
      lines++;
    }
    reader.close();
  } catch (IOException e) {
    e.printStackTrace();
  }
  
   int[][] inputTriangle = new int[lines][lines];
   
  try {
    int j = 0;
    while ((line = reader2.readLine()) != null) {
      linePieces = split(line, " ");
    for (int i = 0; i < linePieces.length; i++) {
            inputTriangle[j][i] = int(linePieces[i]);
        }
        j++;
    }
    reader2.close();
  } catch (IOException e) {
    e.printStackTrace();
  }
  
  return inputTriangle;
}

Altering the probabilities of the evolutionary one, the limit of numGens (number of generations tested) in the while loop, and size (the size of the gene pool), can alter the results obtained. Does anyone have a way to make the evolutionary one more efficient to reach the answer?

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