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  1. #include <cstdlib>
  2. #include <ctime>
  3. #include <iostream>
  4. #include <vector>
  5.  
  6. // nValues is the number of unique values to generate.
  7. // vals points to an array large enough to hold nValues numbers.
  8. // min is the smallest number in the range to generate numbers for.
  9. // max is the largest number in the range to generate numbers for.
  10. // IMPORTANT:  max-min cannot exceed 255.
  11. void generateUniqueRandomValues(unsigned nValues, unsigned* vals, unsigned min, unsigned max)
  12. {
  13.     using std::swap;
  14.     using std::rand;
  15.  
  16.     const unsigned maxElements = 256 ;                  // some arbitrary value.
  17.     unsigned values[maxElements];
  18.  
  19.     const unsigned valuesSize = max - min + 1;          // the number of elements of the values array which we will use.
  20.  
  21.     for (unsigned i = 0; i < valuesSize; ++i)           // fill values with numbers from min to max.
  22.         values[i] = min + i;
  23.  
  24.     for (unsigned i = 0; i < nValues; ++i)
  25.     {
  26.         const unsigned valuesLeft = valuesSize - i;
  27.  
  28.         const unsigned index = rand() % valuesLeft;     // pick a random index for an unused value.
  29.         vals[i] = values[index];                        // store the value in the user-supplied array.
  30.  
  31.         swap(values[index], values[valuesLeft-1]);      // swap the used value with the last unused value.
  32.     }
  33. }
  34.  
  35. int main()
  36. {
  37.     using namespace std;
  38.  
  39.     srand(time(0));
  40.  
  41.     const unsigned nVals = 7;
  42.     const unsigned minVal = 1;
  43.     const unsigned maxVal = 50;
  44.  
  45.     unsigned randValues[nVals];
  46.     generateUniqueRandomValues(nVals, randValues, minVal, maxVal);
  47.  
  48.  
  49.     for (unsigned i = 0; i < nVals; ++i)
  50.         cout << "#" << i+1 << ": " << randValues[i] << '\n' ;
  51. }
Success #stdin #stdout 0s 3340KB
comments (?)
stdin 
Standard input is empty
stdout 
#1: 18
#2: 28
#3: 15
#4: 2
#5: 17
#6: 8
#7: 35
https://ideone.com/DhbCGp
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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