Codeforces Round #285 (Div.1) A Misha and Forest
水题水题水……
题意：给你一些点，给出他们连通了多少个点以及这些点的下标的异或值，让你找出一个图
题解：拓扑排序一发
代码:
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <vector>
#include <queue>
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
const int maxn = pow(2,16)+10;
vector<pair<ll,ll> >ans;
queue<ll> q;
int d[maxn],v[maxn];
bool u[maxn];
int n;
int main()
{
#ifndef ONLINE_JUDGE//freopen("F.in","r",stdin);//freopen("F.out","w",stdout);
#endifcin >> n;for(ll i =0;i<n;i++){cin >> d[i]>>v[i];if(d[i]<2){q.push(i);u[i]=1;}}int t,tt,ttt;while(!q.empty()){t = q.front();q.pop();if(d[t]==0)continue;tt=v[t];v[tt] ^=t;d[t]--;d[tt]--;ans.push_back(make_pair(t,tt));if(d[tt]<2 && !u[tt]){q.push(tt);u[tt]=1;}}cout << ans.size() << endl;for(auto a:ans){cout << a.first <<" " << a.second << endl;}return 0;
}
