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  1. #include <iostream>
  2. #include <cstdlib>
  3.  
  4. using namespace std;
  5. #define max_size 20
  6.  
  7. int partition(int a[], int start, int end){
  8.   int i,j,pivot,temp;
  9.  
  10.   pivot = a[end]; //select last elem as the pivot
  11.   i = start- 1;   // point i and j to before/after start end of the arr
  12.   j= end +1;
  13.  
  14.   while(true){
  15.     //reduce j until we reach an elem that is less than pivot
  16.   	if(a[j] >= pivot){ j= j-1; }	
  17.     //increase i until we reach an elem that is more than pivot
  18. 	if(a[i] <= pivot){ i = i+1; }  
  19.  
  20.  
  21. 	if(i<j){  //swap elems so that it is partitioned
  22. 		  temp = a[j];
  23. 		  a[j] = a[i];
  24. 		  a[i] = temp;
  25.     }
  26.     else{ return j; } //return the boundary for this partition
  27.   }
  28. }
  29.  
  30. void quick_sort(int arr[], int start, int end){
  31.    int boundary;
  32.    if(start<end){
  33. 		 boundary = partition(arr,start,end);
  34.  
  35. 		 quick_sort(arr,start,boundary);
  36.    		 quick_sort(arr,boundary+1, end);
  37.    }
  38.    return;
  39. }
  40.  
  41. int main(){
  42.      int n,i;
  43.  
  44. 	 cout << "Please enter array elements size to sort" << endl;
  45. 	 cin >> n;
  46.  
  47. 	 int a[n];
  48.  
  49. 	 cout << endl <<  "Please enter array of size " << n << endl;
  50.  
  51. 	 for(i=0;i<n;i++){
  52.        	cin >> a[i];		  
  53.      }
  54.  
  55. 	 cout << endl <<  "the array before sorting is: " << endl;
  56.  
  57. 	  for(i=0;i<n;i++){
  58.         cout << a[i] << "\t";
  59.       }	
  60.  
  61.  
  62. 	  /* quick sort */
  63.   	  quick_sort(a,1,n);
  64.  
  65. 	  cout << endl <<  "the array after sorting is: " << endl;
  66.  
  67.       for(i=0;i<n;i++){
  68.         cout << a[i] << "\t";
  69.       }	 
  70.  
  71. 	 system("pause");
  72. 	 return 0;
  73. }
  74.  
Success #stdin #stdout #stderr 0s 3472KB
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stdin
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5
5
4
3
2
1
stdout
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Please enter array elements size to sort

Please enter array of size 5

the array before sorting is: 
5	4	3	2	1	
the array after sorting is: 
-529956	2	1	3	4
stderr
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sh: 1: pause: not found
https://ideone.com/9wUcaF
language:
C++ (gcc 8.3)
created:
8 years ago
visibility:
secret

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