Submission #6419171

---

Source Code Expand

def dfs1(v):
  if len(g[v])==0:
    return 0
  for u in g[v]:
    if checked[u]==0:
      checked[u]=1
      g[u].remove(v)
      g[v].remove(u)
      g2[u].append(v)
      g2[v].append(u)
      dfs1(u)

def dfs2(v):
  if len(g2[v])==0:
    return 0
  for u in g2[v]:
    g2[u].remove(v)
    dfs2(u)
    if cnt[u]%2==1:
      print(u,v)
      cnt[u]+=1
    else:
      print(v,u)
      cnt[v]+=1

n,m=map(int,input().split())
g=[[] for _ in range(n+1)]
g2=[[] for _ in range(n+1)]
cnt=[0]*(n+1)
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):
    if len(g[v])==0:
      continue
    else:
      for u in g[v]:
        print(u,v)
        g[u].remove(v)
        g[v].remove(u)
        cnt[u]+=1
  dfs2(1)

Submission Info

Judge Result