#include <bits/stdc++.h> using namespace std; static int smallest_k(int n){ int k = 0; while (n + k > (1 << k) - 1) k++; return k; } static bool is_pow2(int x){ return x && ((x & (x - 1)) == 0); } vector<int> get_attachment(vector<int> source) { int n = (int)source.size(); int k = smallest_k(n); // assign a unique nonzero k-bit column to each data bit, excluding powers of two vector<int> col(n); int v = 1; for(int i = 0; i < n; i++){ while (v < (1 << k) && is_pow2(v)) v++; col[i] = v; v++; } vector<int> parity(k, 0); // parity[j] = XOR of source[i] for which col[i] has bit j for(int i = 0; i < n; i++){ if(source[i] == 0) continue; for(int j = 0; j < k; j++){ if(col[i] & (1 << j)) parity[j] ^= 1; } } return parity; // appended to source } vector<int> retrieve(vector<int> data) { int N = (int)data.size(); // find n and k? We don't know n directly, but k is small; however in this task // the judge calls retrieve with "source + attachment", so we can deduce k by trying. // easiest: k is the smallest such that N <= 2^k - 1 (since N = n + k and n+k <= 2^k-1) int k = 0; while (N > (1 << k) - 1) k++; int n = N - k; // rebuild same columns used in get_attachment vector<int> col(n); int v = 1; for(int i = 0; i < n; i++){ while (v < (1 << k) && is_pow2(v)) v++; col[i] = v; v++; } // compute syndrome s (k-bit number) int s = 0; // data part for(int i = 0; i < n; i++){ if(data[i]) s ^= col[i]; } // parity/attachment part: parity bit j has column (1<<j) for(int j = 0; j < k; j++){ if(data[n + j]) s ^= (1 << j); } // correct if needed if(s != 0){ if(is_pow2(s)){ // error in parity bit: flip it if you want (not necessary for returning source) int j = __builtin_ctz(s); if(j >= 0 && j < k) data[n + j] ^= 1; } else { // error in a data bit: find which i has col[i] == s for(int i = 0; i < n; i++){ if(col[i] == s){ data[i] ^= 1; break; } } } } // return corrected source bits (first n bits) vector<int> source(n); for(int i = 0; i < n; i++) source[i] = data[i]; return source; }

grader.cpp: In instantiation of 'void shuffle(std::vector<T>&) [with T = Scenario]':
grader.cpp:200:10:   required from here
grader.cpp:28:23: warning: 'void std::random_shuffle(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Scenario*, vector<Scenario> >]' is deprecated: use 'std::shuffle' instead [-Wdeprecated-declarations]
   28 |         random_shuffle(v.begin(), v.end());
      |         ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/13/algorithm:61,
                 from grader.cpp:8:
/usr/include/c++/13/bits/stl_algo.h:4581:5: note: declared here
 4581 |     random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last)
      |     ^~~~~~~~~~~~~~