35 lines
554 B
C++
35 lines
554 B
C++
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#include<bits/stdc++.h>
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using namespace std;
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using ll = long long;
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void solve()
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{
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int n;
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cin>>n;
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int odd_ct=0, even_ct=0;
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for(int i=0; i < n; ++i)
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{
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int x;
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cin>>x;
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if(i%2==0 && x%2!=0)
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even_ct++;
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else if(i%2!=0 && x%2==0)
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odd_ct++;
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}
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if(odd_ct!=even_ct)
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cout<<-1<<endl;
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else
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cout<<odd_ct<<endl;
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}
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int main()
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{
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ios_base::sync_with_stdio(false);
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cin.tie(nullptr);
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int TC = 1;
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cin >> TC;
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cin.ignore();
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while (TC--) solve();
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}
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