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railroad.py
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railroad.py
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input = __import__('sys').stdin.readline
for _ in range(int(input())):
input()
n, m = map(int, input().split())
g = [[0, {}] for _ in range(n+1)]
for _ in range(m):
a, b, w = map(int, input().split())
for _ in range(2):
a, b = b, a
g[a][0] += 1
if b not in g[a][1]: g[a][1][b] = []
g[a][1][b].append(w)
q = []
for i in range(1, n+1):
if g[i][0] == 2: q.append(i)
for i in q:
if g[i][0] == 2:
e = []
for j in g[i][1]:
for k in g[i][1][j]: e.append((j, k))
(a, b), (c, d) = e
g[a][0] -= 1; g[c][0] -= 1
g[i] = [0, {}]
g[a][1].pop(i)
if a != c: g[c][1].pop(i)
g[a][0] += 1; g[c][0] += 1
if c not in g[a][1]: g[a][1][c] = []
if a not in g[c][1]: g[c][1][a] = []
g[a][1][c].append(b+d), g[c][1][a].append(b+d)
if g[a][0] == 2: q.append(a)
if a != c and g[c][0] == 2: q.append(c)
E = set()
for i in range(1, n+1):
for j in g[i][1]:
for k in g[i][1][j]: E.add((min(i, j), max(i, j), k))
print(len(E))
for e in E: print(*e)
print()