Submission #34897350

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<(int)n;i++)
int read(){int r;scanf("%d",&r);return r;}

int fa[200010];
int d[200010];
int getfa(int v) { return v == fa[v]?v:(fa[v] = getfa(fa[v]));}
vector<int> arr[200010];

int main(){
  int n = read();
  int m = read();
  rep(i,1,n+1) d[i] = read();
  iota(fa+1,fa+n+1,1);
  rep(i,0,m){
    int u = read();
    int v = read();
    d[u]--;
    d[v]--;
    int fu = getfa(u);
    int fv = getfa(v);
    if(fu == fv){
      printf("-1\n");
      return 0;
    }
    fa[fu] = fv;
  }
  rep(i,1,n+1){
    if(d[i] < 0){
      printf("-1\n");
      return 0;
    }
    int fi = getfa(i);
    rep(t,0,d[i]) arr[fi].push_back(i);
  }
  vector<int> e1; // equal 1
  vector<int> g1; // greater than 1
  rep(i,1,n+1) if(i == getfa(i)) {
    if(!arr[i].size()){
      printf("-1\n");
      return 0;
    }
    (arr[i].size() == 1?e1:g1).push_back(i);
  }

  vector<pair<int,int>>ans;
  while(e1.size() && g1.size()){
    int pi = e1.back();
    int pj = g1.back();
    ans.push_back({arr[pi].back(),arr[pj].back()});
    e1.pop_back();
    arr[pj].pop_back();
    if(arr[pj].size() == 1){ // 大于1变成等于1
      g1.pop_back();
      e1.push_back(pj);
    }
  }
  if(g1.size() || 2 != (int)e1.size()){
    printf("-1\n");
    return 0;
  }
  ans.push_back({arr[e1[0]].back(),arr[e1[1]].back()});
  for(auto[u,v]:ans) printf("%d %d\n",u,v);
  return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int read()’:
./Main.cpp:4:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
    4 | int read(){int r;scanf("%d",&r);return r;}
      |                  ~~~~~^~~~~~~~~

Judge Result