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  1. #include <iostream>
  2. #include <vector>
  3. #include <algorithm>
  4. #include <math.h>
  5.  
  6. using namespace std;
  7.  
  8. // to use user-defined comparison for sorting,
  9. // the user needs to provide a function that 
  10. // returns true when the left argument should
  11. // go earlier than the right argument (so for
  12. // increasing order the comparison function 
  13. // returns true if i<j);
  14. // this function ensures 3 rules
  15. // 1. even numbers precede odd numbers
  16. // 2. odd numbers should decrease
  17. // 3. even numbers should increase
  18.  
  19. bool is_less(int i, int j)
  20. {
  21.   // even numbers go before odd numbers
  22.  
  23.   if ((i%2==0) && (j%2==1))
  24.     return true;
  25.  
  26.   // even numbers should increase
  27.  
  28.   if ((i%2==0) && (j%2==0))
  29.     return (i<j);
  30.  
  31.   // odd numbers should decrease
  32.  
  33.   if ((i%2==1) && (j%2==1))
  34.     return (i>j);
  35.  
  36.   // otherwise, i should not be forced to
  37.   // precede j
  38.  
  39.   return false;
  40. }
  41.  
  42. int main()
  43. {
  44.   int i;
  45.   int n = 18;
  46.  
  47.   // initialize random number generator with random seed 123
  48.  
  49.   srand48(123);
  50.  
  51.   // two vectors of n elements of type int
  52.  
  53.   vector<int> v(n);
  54.  
  55.   // generate both vectors random, each variable from 
  56.   // uniform distribution over interval {0, ..., 99}
  57.  
  58.   for (i=0; i<n; i++)
  59.     v[i] = drand48()*100;   
  60.  
  61.   // print out the vector
  62.  
  63.   cout << "initial vector:" << endl;
  64.   for (i=0; i<n; i++)
  65.     cout << "   " << v[i] << endl;
  66.  
  67.   // sort the vector (ascending order)
  68.   // (v.begin() and v.end() indicate that the sorting
  69.   // should consider the entire vector from its start
  70.   // on the left until the end on the right)
  71.  
  72.   sort( v.begin(), v.end(), is_less);
  73.  
  74.   // print out the vector
  75.  
  76.   cout << "sorted vector:" << endl;
  77.   for (i=0; i<n; i++)
  78.     cout << "   " << v[i] << endl;
  79.  
  80.   // return from main with 0
  81.  
  82.   return 0;
  83. }
  84.  
Success #stdin #stdout 0.01s 2816KB
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stdin
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Standard input is empty
stdout
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initial vector:
   27
   41
   92
   12
   12
   34
   62
   83
   69
   15
   78
   36
   93
   14
   85
   11
   81
   39
sorted vector:
   12
   12
   14
   34
   36
   62
   78
   92
   93
   85
   83
   81
   69
   41
   39
   27
   15
   11
https://ideone.com/y7iQQ
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
secret

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