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  1. #include <iostream>
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4.  
  5. int helpInverse(int A[],int start,int mid,int end){
  6.  
  7. 	int len=end-start+1;
  8.  
  9. 	vector<int>temp(len+1);
  10. 	int i=start,j=mid+1;
  11. 	int cnt=0,x=0;
  12. 	while(i<=mid && j<=end){
  13.  
  14. 		if(A[i]<=A[j]){
  15. 				temp[x++]=A[i++];
  16. 		}else{
  17. 				temp[x++]=A[j++];
  18. 				cnt+=(mid-i)+1;
  19. 		}
  20.  
  21. 	}
  22.  
  23. 	while(i<=mid){
  24. 		temp[x++]=A[i++];
  25. 	}
  26.  
  27. 	while(j<=end){
  28. 		temp[x++]=A[j++];
  29. 	}
  30.  
  31. 	int t=start;
  32. 	for(int i=0;i<x;++i){
  33. 		A[t++]=temp[i];
  34. 	}
  35.  
  36. return cnt;
  37. }
  38.  
  39. int countInversions(int A[],int start,int end){
  40. 		int x=0;
  41. 		if(start<end){
  42.  
  43. 			int mid=(start+end)/2;
  44.  
  45. 	  		x+=countInversions(A,start,mid);
  46. 			x+=countInversions(A,mid+1,end);
  47. 			x+=helpInverse(A,start,mid,end);
  48. 		}
  49. 		return x;
  50. }
  51.  
  52.  
  53. int main() {
  54. 	// your code
  55. 	int arr[5]={1, 20, 6, 4, 5};
  56. 	cout<<"ans: "<<countInversions(arr,0,4)<<endl;
  57.  
  58. 	return 0;
  59. }
Success #stdin #stdout 0s 3456KB
comments (?)
stdin 
Standard input is empty
stdout 
ans: 5
https://ideone.com/INt2aw
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
secret

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