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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. int main()
  6. {
  7.     int n;
  8.     cin >> n;
  9.     int degree[n], xorsum[n];
  10.     queue <int> Q;
  11.     int used = 0;
  12.     for(int i = 0; i < n; ++i)
  13.     {
  14.     	cin >> degree[i] >> xorsum[i];
  15.     	if (degree[i] == 1)
  16.     		Q.push(i);
  17.     	if (degree[i] == 0)
  18.     	{
  19.     		if (xorsum[i] != 0)
  20.     			assert(false);
  21.     		used++;
  22.     	}
  23.     }
  24.     vector < pair<int, int>  > ans;
  25.     while(!Q.empty())
  26.     {
  27.     	int from = Q.front();
  28.     	Q.pop();
  29.     	used++;
  30.     	if (degree[from] == 0)
  31.     	{
  32.     		if (xorsum[from] != 0)
  33.     			assert(false);
  34.     		continue;
  35.     	}
  36.     	degree[from]--;
  37.     	int to = xorsum[from];
  38.     	xorsum[from] = 0;
  39.     	if (to >= n)
  40.     		assert(false);
  41.     	ans.push_back(make_pair(from, to));
  42.     	xorsum[to] ^= from;
  43.     	if (degree[to] == 0)
  44.     		assert(false);
  45.     	degree[to]--;
  46.     	if (degree[to] == 1)
  47.     		Q.push(to);
  48.     }
  49.     if (used != n)
  50.     	assert(false);
  51.     cout << ans.size() << endl;
  52.     for(size_t i = 0; i < ans.size(); ++i)
  53.     	cout << ans[i].first << " " << ans[i].second << endl;
  54. 	return 0;
  55.  
  56. }
Runtime error #stdin #stdout 0s 3100KB
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Standard input is empty
stdout
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Standard output is empty
https://ideone.com/H7Vawi
language:
C++ (gcc 8.3)
created:
9 years ago
visibility:
public

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