command: g++ -std=c++20 -O2 -pipe main.cpp -o main

target: optimize runtime without changing outputs

baseline_complexity: O(n^2) due to redundant nested loop

expected_better_complexity: O(n)

oracle_acceptance: full mark only

[System] You are an expert C++20 performance optimizer. Preserve stdin/stdout behavior exactly. Prefer simple, readable algorithmic improvements over micro-optimizations. Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

[User]
Task: optimize this correct but intentionally inefficient C++20 program. Keep the same input and output behavior.

Original program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n;cin>>n;vector<long long>a(n);for(int i=0;i<n;i++)cin>>a[i];long long ans=0;for(int i=0;i<n;i++){for(int j=0;j<=i;j++){if(i==j && a[j]%2==0) ans+=a[j];}}cout<<ans<<"\n";}
```

Visible tests:
sample_1 stdin:
```text
5
1 2 3 4 6
```
Expected stdout:
```text
12
```

prompt:
SYSTEM: You are an expert C++20 performance optimizer. Preserve stdin/stdout behavior exactly. Prefer simple, readable algorithmic improvements over micro-optimizations. Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

USER: Task: optimize this correct but intentionally inefficient C++20 program. Keep the same input and output behavior.

Original program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n;cin>>n;vector<long long>a(n);for(int i=0;i<n;i++)cin>>a[i];long long ans=0;for(int i=0;i<n;i++){for(int j=0;j<=i;j++){if(i==j && a[j]%2==0) ans+=a[j];}}cout<<ans<<"\n";}
```

Visible tests:
sample_1 stdin:
```text
5
1 2 3 4 6
```
Expected stdout:
```text
12
```


baseline_complexity: O(nq) range sums

expected_better_complexity: O(n+q) with prefix sums

[User]
Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

Task: optimize this correct but intentionally inefficient C++20 program. Keep the same input and output behavior.

Original program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n,q;cin>>n>>q;vector<long long>a(n+1);for(int i=1;i<=n;i++)cin>>a[i];while(q--){int l,r;cin>>l>>r;long long s=0;for(int i=1;i<=n;i++){if(l<=i && i<=r)s+=a[i];}cout<<s<<"\n";}}
```

Visible tests:
sample_1 stdin:
```text
5 3
2 4 6 8 10
1 3
2 5
4 4
```
Expected stdout:
```text
12
28
8
```

prompt:
USER: Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

Task: optimize this correct but intentionally inefficient C++20 program. Keep the same input and output behavior.

Original program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n,q;cin>>n>>q;vector<long long>a(n+1);for(int i=1;i<=n;i++)cin>>a[i];while(q--){int l,r;cin>>l>>r;long long s=0;for(int i=1;i<=n;i++){if(l<=i && i<=r)s+=a[i];}cout<<s<<"\n";}}
```

Visible tests:
sample_1 stdin:
```text
5 3
2 4 6 8 10
1 3
2 5
4 4
```
Expected stdout:
```text
12
28
8
```


baseline_complexity: O(n^2) pair enumeration

expected_better_complexity: O(n) average with hash map or O(n log n) with sorting

[System] You are an expert C++20 performance optimizer. Preserve stdin/stdout behavior exactly. Prefer simple, readable algorithmic improvements over micro-optimizations. Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

[User]
Make the following C++20 solution asymptotically faster if possible, while preserving the exact interface and outputs.

Task: optimize this correct but intentionally inefficient C++20 program. Keep the same input and output behavior.

Original program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n,k;cin>>n>>k;vector<int>a(n);for(int&i:a)cin>>i;long long ans=0;for(int i=0;i<n;i++){for(int j=0;j<n;j++){if(i<j && a[i]+a[j]==k)ans++;}}cout<<ans<<"\n";}
```

Visible tests:
sample_1 stdin:
```text
6 7
1 6 2 5 3 4
```
Expected stdout:
```text
3
```

prompt:
SYSTEM: You are an expert C++20 performance optimizer. Preserve stdin/stdout behavior exactly. Prefer simple, readable algorithmic improvements over micro-optimizations. Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

USER: Make the following C++20 solution asymptotically faster if possible, while preserving the exact interface and outputs.

Task: optimize this correct but intentionally inefficient C++20 program. Keep the same input and output behavior.

Original program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n,k;cin>>n>>k;vector<int>a(n);for(int&i:a)cin>>i;long long ans=0;for(int i=0;i<n;i++){for(int j=0;j<n;j++){if(i<j && a[i]+a[j]==k)ans++;}}cout<<ans<<"\n";}
```

Visible tests:
sample_1 stdin:
```text
6 7
1 6 2 5 3 4
```
Expected stdout:
```text
3
```


stdin:
6
red blue green blue red yellow

stdout: blue

baseline_complexity: O(n^2) previous-item scan

expected_better_complexity: O(n) average with unordered_set

[System] Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

[User]
optimization_request:
  language: C++20
  objective: reduce runtime while preserving behavior
  checker: exact stdout after trimming trailing whitespace
  task_id: dummy_pie_cpp_0004_first_repeated

source_code:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n;cin>>n;vector<string>s(n);for(auto&x:s)cin>>x;string ans="NONE";for(int i=0;i<n;i++){bool seen=false;for(int j=0;j<i;j++){if(s[j]==s[i])seen=true;}if(seen){ans=s[i];break;}}cout<<ans<<"\n";}
```

visible_tests:
sample_1 stdin:
```text
6
red blue green blue red yellow
```
Expected stdout:
```text
blue
```

prompt:
SYSTEM: Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

USER: optimization_request:
  language: C++20
  objective: reduce runtime while preserving behavior
  checker: exact stdout after trimming trailing whitespace
  task_id: dummy_pie_cpp_0004_first_repeated

source_code:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n;cin>>n;vector<string>s(n);for(auto&x:s)cin>>x;string ans="NONE";for(int i=0;i<n;i++){bool seen=false;for(int j=0;j<i;j++){if(s[j]==s[i])seen=true;}if(seen){ans=s[i];break;}}cout<<ans<<"\n";}
```

visible_tests:
sample_1 stdin:
```text
6
red blue green blue red yellow
```
Expected stdout:
```text
blue
```


baseline_complexity: O(nm^2) redundant row maximum scan

expected_better_complexity: O(nm)

[User]
Can you make this C++ program faster without changing what it reads or prints? Please keep it C++20.

Program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n,m;cin>>n>>m;vector<vector<int>>a(n,vector<int>(m));for(int i=0;i<n;i++)for(int j=0;j<m;j++)cin>>a[i][j];for(int i=0;i<n;i++){int best=INT_MIN;for(int j=0;j<m;j++){for(int k=0;k<m;k++){if(k==j)best=max(best,a[i][k]);}}cout<<best<<(i+1==n?'\n':' ');} }
```

Try it on this visible test before returning it:
sample_1 stdin:
```text
3 4
1 9 2 3
4 5 6 7
-3 -8 -1 -2
```
Expected stdout:
```text
9 7 -1
```

Answer format: Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.

prompt:
USER: Can you make this C++ program faster without changing what it reads or prints? Please keep it C++20.

Program:
```cpp
#include <iostream>
#include <vector>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <climits>
#include <algorithm>
using namespace std;
int main(){ios::sync_with_stdio(false);cin.tie(nullptr);int n,m;cin>>n>>m;vector<vector<int>>a(n,vector<int>(m));for(int i=0;i<n;i++)for(int j=0;j<m;j++)cin>>a[i][j];for(int i=0;i<n;i++){int best=INT_MIN;for(int j=0;j<m;j++){for(int k=0;k<m;k++){if(k==j)best=max(best,a[i][k]);}}cout<<best<<(i+1==n?'\n':' ');} }
```

Try it on this visible test before returning it:
sample_1 stdin:
```text
3 4
1 9 2 3
4 5 6 7
-3 -8 -1 -2
```
Expected stdout:
```text
9 7 -1
```

Answer format: Return exactly one <reasoning>...</reasoning> block followed by exactly one fenced ```cpp code block containing an optimized C++20 program. Do not include any other text.