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Even array.cpp
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Even array.cpp
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#include<bits/stdc++.h>
#define ll long long int
using namespace std;
int main()
{
int t;
cin>>t;
while(t--)
{
int n;
cin>>n;
int a[n];
for(int i=0; i<n; i++)
{
cin>>a[i];
}
int cnt=0;
for(int i=0; i<n; i++)
{
if(i%2!=a[i]%2)
{
if( i%2==0)
{
for(int j=i+1; j<n; j++)
{
if(a[j]%2==0 && j%2!=0)
{
swap(a[i],a[j]);
cnt++;
break;
}
}
}
else
{
for(int j=i+1; j<n; j++)
{
if(a[j]%2==1 && j%2!=1)
{
swap(a[i],a[j]);
cnt++;
break;
}
}
}
}
}
bool flag=true;
for(int i=0; i<n; i++)
{
if(i%2!=a[i]%2)
{
flag=false;
}
}
if(flag)
cout<<cnt<<endl;
else
cout<<-1<<endl;
}
return 0;
}