Submission #6375519

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Source Code Expand

import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)

N,M = map(int,input().split())
if M&1:
    print(-1)
    exit()

AB = [[int(x) for x in input().split()] for _ in range(M)]

graph = [[] for _ in range(N+1)]
for a,b in AB:
    graph[a].append(b)
    graph[b].append(a)

# まずは全域木をつくる
tree = [set() for _ in range(N+1)]
visited = [False] * (N+1)
q = [1]
while q:
    x = q.pop()
    for y in graph[x]:
        if visited[y]:
            continue
        visited[y] = True
        tree[x].add(y)
        tree[y].add(x)
        q.append(y)

answer = []
out_deg = [0] * (N+1)
# 木を残して適当に決める
for a,b in AB:
    if b in tree[a]:
        continue
    answer.append('{} {}'.format(a,b))
    out_deg[a] += 1

def dfs(x = 1,parent = None):
    for y in tree[x]:
        if y == parent:
            continue
        dfs(y,x)
        if out_deg[y] & 1:
            answer.append('{} {}'.format(y,x))
            out_deg[y] += 1
        else:
            answer.append('{} {}'.format(x,y))
            out_deg[x] += 1

dfs()

print('\n'.join(answer))

Submission Info

Judge Result