func_code_string: #include <bits/stdc++.h>   using namespace std;   int main(int argc, char **argv) {     ios_base::sync_with_stdio(false);     cin.tie(0);     ;     int n;     cin >> n;     vector<int> indeg(n);     queue<int> deg1;     vector<int> xorV(n);     for (int i = 0; i < n; i++) {       cin >> indeg[i] >> xorV[i];       if (indeg[i] == 1) deg1.push(i);     }     set<pair<int, int> > edges;     while (deg1.size() > 0) {       int v = deg1.front();       deg1.pop();       int u = xorV[v];       if (--indeg[u] == 1) deg1.push(u);       if (indeg[u] > 0) xorV[u] ^= v;       if (v > u) swap(u, v);       edges.insert({u, v});     }     cout << edges.size() << endl;     for (auto &edg : edges) {       cout << edg.first <<     << edg.second << endl;     }     return 0;   }   