Submission #6625044

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Source Code Expand

import sys
sys.setrecursionlimit(10**9)

def dfs1(v):
  for u in g[v]:
    if checked[u]==0:
      checked[u]=1
      g2[v].append(u)
      g3[v].append(u)
      g3[u].append(v)
      dfs1(u)
      
def dfs2(v):
  for u in g2[v]:
    if checked[u]==0:
      checked[u]=1
      dfs2(u)
      if cnt[u]%2==1:
        ans.append((u,v))
        cnt[u]+=1
      else:
        ans.append((v,u))
        cnt[v]+=1
      
n,m=map(int,input().split())
g=[[] for _ in range(n+1)]
g2=[[] for _ in range(n+1)]
g3=[[] for _ in range(n+1)]
cnt=[0]*(n+1)
ans=[]
ansset=set()
for _ in range(m):
  a,b=map(int,input().split())
  g[a].append(b)
  g[b].append(a)
if m%2==1:
  print(-1)
else:
  checked=[0]*(n+1)
  checked[1]=1
  dfs1(1)
  for v in range(1,n+1):
    for u in g[v]:
      if u not in g3[v]:
        if (u,v) not in ansset:
          ans.append((v,u))
          ansset.add((v,u))
          cnt[v]+=1
  checked=[0]*(n+1)
  checked[1]=1
  dfs2(1)
  for v,u in ans:
    print(v,u)

Submission Info

Judge Result