Counting Inversion from problem https://codeforces.com/contest/911/problem/D

countInversion.cpp

# include <iostream>
# include <algorithm>
# include <string>

using namespace std;


bool isOdd(int number){
	return number&1;
}

int changePairity(int number){
	return number^1;
}

int* inputNumbers(int N){
	int* array = new int[N];
	for(int i=0;i<N;i++){
		cin>>array[i];
	}
	return array;
}

int findPairityOfInversion(int* array, int N){
	int pairityOfInversion;
	for(int i=0;i<N;i++){
	 	for(int j=i+1;j<N;j++){
	 		pairityOfInversion ^= (array[i]>array[j]);
	 	}
	 }
	 return pairityOfInversion;
}

int main() {

	 int N;
	 cin>>N;
	 
	 int* array = inputNumbers(N);
	
	 int pairityOfInversion = findPairityOfInversion(array, N);
	  
	 int queries;
	 cin>>queries;
	 string result[queries];
	 
	 for(int i=0;i<queries;i++){
	 	
	 	int L,R;
	 	cin>>L>>R;	 	 

	 	int numberOfSwaps = ((R-L+1) * (R-L))>>1; // equivalent to ((R-L+1) * (R-L))/2
	 	 
	 	if(isOdd(numberOfSwaps)) {	 	 
	 		pairityOfInversion = changePairity(pairityOfInversion);	 	 
	 	}
	 	
	 	if(isOdd(pairityOfInversion)){
	 		result[i] = "odd";
	 	} else {
	 		result[i] = "even";
	 	}
	 }

	 for(int i=0;i<queries;i++){
	 	cout<<result[i]<<endl;
	 }
 
}