Problem of the Day
A new programming or logic puzzle every Mon-Fri

Comments:

• Anonymous - 9 years, 8 months ago

  cool

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• Driphter - 9 years, 8 months ago

  Clojure!

  I wasn't sure if the "between" in the requirements was supposed to be inclusive or exclusive, so I did both.

  (defn- rand-sum-inclusive*
    [k n]
    (if (= 1 k)
      [n]
      (let [r (cond
               (pos? n) (rand-int (inc n))
               (neg? n) (rand-int (dec n))
               :else 0)]
        (concat [r] (rand-sum-inclusive* (dec k) (- n r))))))
  
  (defn rand-sum-inclusive
    [k n]
    {:pre [(number? k) (number? n)
           (pos? k)]
     :post [(= n (apply + %))]}
    (rand-sum-inclusive* k n))
  
  (defn- rand-sum-exclusive*
    [k n]
    (if (= 1 k)
      [n]
      (let [r (if (pos? n)
                (inc (rand-int (- n (dec k))))
                (dec (rand-int (+ n (inc k)))))]
        (concat [r] (rand-sum-exclusive* (dec k) (- n r))))))
  
  (defn rand-sum-exclusive
    [k n]
    {:pre [(number? k) (number? n)
           (pos? k)
           (or (and (pos? n) (not (neg? (- n k))))
               (and (neg? n) (not (pos? (+ n k)))))]
     :post [(= n (apply + %))]}
    (rand-sum-exclusive* k n))
  

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• Anonymous - 9 years, 8 months ago

  Using HTML + JS (with jquery) https://jsfiddle.net/k0f8k3va/1/

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• David - 9 years, 4 months ago

  #include <stdio.h>
  #include <stdlib.h>
  #include <time.h>
  
  //modify the passed array parameter to contain the k integers from 0 to n, inclusive, that add up to n
  //this function must be should k be allowed to be larger than n.
  //I have made the design decision to allow earlier selected values to remain as unbound as possible
  //therefore, I will keep a checksum
  void randSum(int* arr, unsigned int k, unsigned int n) {
      int maxRemaining = n;
      int count = 0;
      srand(time(NULL));
      //This use of array length without checking length is susceptible to a buffer overflow from a malicious user of the function
      while(count < k) {
          arr[count] = rand() % (maxRemaining + 1);
          maxRemaining -= arr[count];
          count++;
      }
  
  // Below is for output visibility sake
      printf("n = %i: ", n);
      //I am printing because I feel a touch lazy.
      //A better version still would have a return type that enumerates possible errors.
      for(count = 0; count < k; count++) {
          printf("%i", arr[count]);
          if(count < k-1) printf(", ");
      }
      printf("\n");
  }
  
  
  int main(int argc, char const *argv[])
  {
      int* array = (int*) malloc(5 * sizeof(int));
  
      randSum(array, 5, 10);
      randSum(array, 5, 3);
      randSum(array, 5, 5);
      free(array);
      return 0;
  }
  

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