Buggy python submission (verdict: Runtime Error):
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          iti = (j)-zan[a][1]
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          zan[i] = (ino,iti)
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(ano,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Fixed submission:
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          iti = (j)-zan[a][1]
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          kime = a
          zan[i] = (ino,iti)
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(kime,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Buggy python submission (verdict: Runtime Error):
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          zan[i] = (ino,(j)-zan[a][1])
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(ano,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Fixed submission:
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          iti = (j)-zan[a][1]
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          kime = a
          zan[i] = (ino,iti)
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(kime,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Buggy python submission (verdict: Runtime Error):
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          zan[i][0] = ino
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(ano,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Fixed submission:
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          iti = (j)-zan[a][1]
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          kime = a
          zan[i] = (ino,iti)
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(kime,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Buggy python submission (verdict: Runtime Error):
import copy
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
cost2 = copy.deepcopy(cost)
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          zan[i][0] = ino
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(ano,0)]
  while len(tan):
      i,j = tan.pop()
      for a,b in cost2[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)

Fixed submission:
n,m = map(int,input().split())
p = []
for i in range(m):
    x1,y1,z1,=[int(i) for i in input().split()]
    p.append([x1-1,y1-1,z1])
cost = [[] for i in range(n)]
for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
zan = [[float("inf"),float("inf")] for i in range(n)]
zan[0] = (1,0)
tan =[(0,0)]
e = 0
while len(tan):
  i,j = tan.pop()
  for a,b in cost[i]:
    if (zan[a][0] != float("inf")):
      if abs((j)-zan[a][1]) == 1:
        pass
      elif ((j)-zan[a][1])%2 == 1:
        if zan[a][0] != b - zan[i][0]:
          e=1
          tan = []
          break
      else:
        e = 2
        if zan[a][0] != b - zan[i][0]:
          e = 3
          x = zan[a][0] + zan[i][0]
          if (b-x)% 2 != 0:
            e = 4
            tan = []
            break
          ano = zan[a][0] + (b-x)//2
          ino = zan[i][0] + (b-x)//2
          iti = (j)-zan[a][1]
          zan = [[float("inf"),float("inf")] for i in range(n)]
          zan[a] = (ano,0)
          kime = a
          zan[i] = (ino,iti)
          tan = []
          break
    zan[a] = (b - zan[i][0],j+1)
    tan.append((a,j+1))
  cost[i] = []
if e == 1:
  print(0)
elif e == 2:
  f = 0
  for i in range(n):
    if zan[i][0]<= 0:
      f = 1
      break
  if f == 0:
    print(1)
  else:
    print(0)
elif e == 4:
  print(0)
elif e == 0:
  syou =0
  f = 0
  dai = float("inf")
  for a,b in zan:
    if b %2 ==0:
      if a < 1:
        syou = max(syou,-a+1)
    else:
      if a > 0:
        dai = min(dai,a-1)
      else:
        f = 1
        break
  if f == 1:
    print(0)
  else:
    if dai >= syou:
      print(dai-syou+1)
    else:
      print(0)
elif e == 3:
  tan =[(kime,0)]
  cost = [[] for i in range(n)]
  for path in p:
    cost[path[0]].append((path[1],path[2]))
    cost[path[1]].append((path[0],path[2]))
  while len(tan):
      i,j = tan.pop()
      for a,b in cost[i]:
        if (zan[a][0] != float("inf")):
          if abs((j)-zan[a][1]) == 1:
            pass
          elif ((j)-zan[a][1])%2 == 1:
            if zan[a][0] != b - zan[i][0]:
              e=1
              tan = []
              break
          else:
            if zan[a][0] != b - zan[i][0]:
              e = 1
              break
        zan[a] = (b - zan[i][0],j+1)
        tan.append((a,j+1))
      cost[i] = []
  if e == 1:
    print(0)
  else:
    f = 0
    for i in range(n):
      if zan[i][0]<= 0:
        f = 1
        break
    if f == 0:
      print(1)
    else:
      print(0)