func_code_string: #include <bits/stdc++.h>   int main() {     int n, m;     scanf( %d%d , &n, &m);     std::vector<std::vector<int>> graph(n);     for (int i = 0; i < m; ++i) {       int a, b;       scanf( %d%d , &a, &b);       a--;       b--;       graph.at(a).push_back(b);       graph.at(b).push_back(a);     }     std::vector<int> color(n, -1);     bool ok = true;     for (int s = 0; s < n && ok; ++s) {       if (!~color[s]) {         std::vector<int> queue;         queue.push_back(s);         color[s] = 0;         for (int h = 0; h < static_cast<int>(queue.size()); ++h) {           auto u = queue[h];           for (int v : graph.at(u)) {             if (!~color[v]) {               color[v] = color[u] ^ 1;               queue.push_back(v);             }             ok &= color[u] != color[v];           }         }       }     }     if (ok) {       std::vector<std::vector<int>> result(2);       for (int i = 0; i < n; ++i) {         result[color[i]].push_back(i);       }       for (int i = 0; i < 2; ++i) {         printf( %d n , static_cast<int>(result[i].size()));         for (auto&& v : result[i]) {           printf( %d  , v + 1);         }         puts(  );       }     } else {       puts( -1 );     }   }   