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  1. #include <stdlib.h>
  2. #include <cmath>
  3. #include <iostream>
  4. using namespace std;
  5.  
  6. int rangeRandomAlg1 (int min, int max)
  7. {
  8.     static const double s_invRandMax = 1.0/((double)RAND_MAX + 1.0);
  9.     return min + (int)(((double)(max + 1 - min))*rand()*s_invRandMax);
  10. }
  11.  
  12. int rangeRandomAlg2 (int min, int max)
  13. {
  14.     int n = max - min + 1;
  15.     int remainder = RAND_MAX % n;
  16.     int x, output;
  17.     do
  18.     {
  19.         x = rand();
  20.         output = x % n;
  21.     } while (x > RAND_MAX - remainder);
  22.     return min + output;
  23. }
  24.  
  25. int main ()
  26. {
  27.     static const int s_numBuckets = 10; // the number of "buckets"
  28.     static const int s_numBalls = 100; // the number of "balls"
  29.     int buckets[s_numBuckets];
  30.     double idealProbPerBucket = 1.0/s_numBuckets;
  31.     double maxDevFromIdealProb;
  32.  
  33.     // Testing algorithm 1
  34.     cout << "Testing with floating-point mapping:" << endl;
  35.     for (int i = 0; i < s_numBuckets; i++)
  36.     {
  37.         buckets[i] = 0;
  38.     }
  39.     srand(0);
  40.     for (int i = 0; i < s_numBalls; i++)
  41.     {
  42.         buckets[rangeRandomAlg1(0, s_numBuckets - 1)]++;
  43.     }
  44.     maxDevFromIdealProb = -1.0;
  45.     for (int i = 0; i < s_numBuckets; i++)
  46.     {
  47.         double prob = ((double)buckets[i])/s_numBalls;
  48.         cout << "Probability for bucket #" << i << ": " << prob << endl;
  49.  
  50.         double devFromIdealProb = fabs(prob - idealProbPerBucket);
  51.         if ( devFromIdealProb > maxDevFromIdealProb )
  52.         {
  53.             maxDevFromIdealProb = devFromIdealProb;
  54.         }
  55.     }
  56.     cout << ">>> Maximum deviation from the ideal probability: " << maxDevFromIdealProb << endl;
  57.     cout << endl;
  58.  
  59.     // Testing algorithm 2
  60.     cout << "Testing with Java's algorithm:" << endl;
  61.     for (int i = 0; i < s_numBuckets; i++)
  62.     {
  63.         buckets[i] = 0;
  64.     }
  65.     srand(0);
  66.     for (int i = 0; i < s_numBalls; i++)
  67.     {
  68.         buckets[rangeRandomAlg2(0, s_numBuckets - 1)]++;
  69.     }
  70.     maxDevFromIdealProb = -1.0;
  71.     for (int i = 0; i < s_numBuckets; i++)
  72.     {
  73.         double prob = ((double)buckets[i])/s_numBalls;
  74.         cout << "Probability for bucket #" << i << ": " << prob << endl;
  75.  
  76.         double devFromIdealProb = fabs(prob - idealProbPerBucket);
  77.         if ( devFromIdealProb > maxDevFromIdealProb )
  78.         {
  79.             maxDevFromIdealProb = devFromIdealProb;
  80.         }
  81.     }
  82.     cout << ">>> Maximum deviation from the ideal probability: " << maxDevFromIdealProb << endl;
  83.  
  84.     return 0;
  85. }
Success #stdin #stdout 0.01s 2684KB
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Standard input is empty
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Testing with floating-point mapping:
Probability for bucket #0: 0.07
Probability for bucket #1: 0.08
Probability for bucket #2: 0.1
Probability for bucket #3: 0.1
Probability for bucket #4: 0.08
Probability for bucket #5: 0.1
Probability for bucket #6: 0.12
Probability for bucket #7: 0.09
Probability for bucket #8: 0.12
Probability for bucket #9: 0.14
>>> Maximum deviation from the ideal probability: 0.04

Testing with Java's algorithm:
Probability for bucket #0: 0.08
Probability for bucket #1: 0.07
Probability for bucket #2: 0.12
Probability for bucket #3: 0.11
Probability for bucket #4: 0.1
Probability for bucket #5: 0.09
Probability for bucket #6: 0.15
Probability for bucket #7: 0.1
Probability for bucket #8: 0.07
Probability for bucket #9: 0.11
>>> Maximum deviation from the ideal probability: 0.05
https://ideone.com/oPhqK
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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