Buggy python submission (verdict: Runtime Error):
visited=set()
success=1
def dfs(b,graph, node):
  global visited
  global success
  if node not in visited:
    visited.add(node)
    for counter in range(len(graph[node-1][0])):
      if b[graph[node-1][0][counter]-1]==10000000000000000000:
        b[graph[node-1][0][counter]-1]=b[node-1]+graph[node-1][1][counter]
      else:
        if  b[graph[node-1][0][counter]-1]!=b[node-1]+graph[node-1][1][counter]:
          success=0
      dfs(b,graph, graph[node-1][0][counter])
      
n,m=map(int,input().split())
a=[]
b=[10000000000000000000]*n
for i in range(n):
  a.append([[],[]])
done=[0]*n
for i in range(m):
  l,r,d=map(int,input().split())
  a[l-1][0].append(r)
  a[l-1][1].append(d)
  a[r-1][0].append(l)
  a[r-1][1].append(-d)
current=[1]
for i in range(n):
  if i+1 in visited:
    continue
  b=[10000000000000000000]*n
  b[i]=0
  dfs(b,a,i+1)
if success==0:
  print('No')
else:
  print('Yes')

Fixed submission:
visited=set()
success=1
import sys
sys.setrecursionlimit(1000000)
def dfs(graph, node):
  global visited
  global b
  global success
  if node not in visited:
    visited.add(node)
    for counter in range(len(graph[node-1][0])):
      if b[graph[node-1][0][counter]-1]==10000000000000000000:
        b[graph[node-1][0][counter]-1]=b[node-1]+graph[node-1][1][counter]
      else:
        if  b[graph[node-1][0][counter]-1]!=b[node-1]+graph[node-1][1][counter]:
          success=0
      dfs(graph, graph[node-1][0][counter])
      
n,m=map(int,input().split())
a=[]
b=[10000000000000000000]*n
for i in range(n):
  a.append([[],[]])
done=[0]*n
for i in range(m):
  l,r,d=map(int,input().split())
  a[l-1][0].append(r)
  a[l-1][1].append(d)
  a[r-1][0].append(l)
  a[r-1][1].append(-d)
current=[1]
for i in range(n):
  if i+1 in visited:
    continue
  b[i]=0
  dfs(a,i+1)
if success==0:
  print('No')
else:
  print('Yes')

Buggy python submission (verdict: Runtime Error):
visited=set()
success=1
def dfs(b,graph, node):
  global visited
  if node not in visited:
    visited.add(node)
    for counter in range(len(graph[node-1][0])):
      if b[graph[node-1][0][counter]-1]==10000000000000000000:
        b[graph[node-1][0][counter]-1]=b[node-1]+graph[node-1][1][counter]
      else:
        if  b[graph[node-1][0][counter]-1]!=b[node-1]+graph[node-1][1][counter]:
          global success
          success=0
      dfs(b,graph, graph[node-1][0][counter])
n,m=map(int,input().split())
a=[]
b=[10000000000000000000]*n
for i in range(n):
  a.append([[],[]])
done=[0]*n
for i in range(m):
  l,r,d=map(int,input().split())
  a[l-1][0].append(r)
  a[l-1][1].append(d)
  a[r-1][0].append(l)
  a[r-1][1].append(-d)
current=[1]
for i in range(n):
  b=[10000000000000000000]*n
  b[i]=0
  dfs(b,a,i+1)
if success==0:
  print('No')
else:
  print('Yes')

Fixed submission:
visited=set()
success=1
import sys
sys.setrecursionlimit(1000000)
def dfs(graph, node):
  global visited
  global b
  global success
  if node not in visited:
    visited.add(node)
    for counter in range(len(graph[node-1][0])):
      if b[graph[node-1][0][counter]-1]==10000000000000000000:
        b[graph[node-1][0][counter]-1]=b[node-1]+graph[node-1][1][counter]
      else:
        if  b[graph[node-1][0][counter]-1]!=b[node-1]+graph[node-1][1][counter]:
          success=0
      dfs(graph, graph[node-1][0][counter])
      
n,m=map(int,input().split())
a=[]
b=[10000000000000000000]*n
for i in range(n):
  a.append([[],[]])
done=[0]*n
for i in range(m):
  l,r,d=map(int,input().split())
  a[l-1][0].append(r)
  a[l-1][1].append(d)
  a[r-1][0].append(l)
  a[r-1][1].append(-d)
current=[1]
for i in range(n):
  if i+1 in visited:
    continue
  b[i]=0
  dfs(a,i+1)
if success==0:
  print('No')
else:
  print('Yes')

Buggy python submission (verdict: Runtime Error):
visited=set()
success=1
def dfs(graph, node):
  global b
  global visited
  if node not in visited:
    visited.add(node)
    for counter in range(len(graph[node-1][0])):
      if b[graph[node-1][0][counter]-1]==10000000000000000000:
        b[graph[node-1][0][counter]-1]=b[node-1]+graph[node-1][1][counter]
      else:
        if  b[graph[node-1][0][counter]-1]!=b[node-1]+graph[node-1][1][counter]:
          global success
          success=0
      dfs(graph, graph[node-1][0][counter])
n,m=map(int,input().split())
a=[]
b=[10000000000000000000]*n
for i in range(n):
  a.append([[],[]])
done=[0]*n
for i in range(m):
  l,r,d=map(int,input().split())
  a[l-1][0].append(r)
  a[l-1][1].append(d)
  a[r-1][0].append(l)
  a[r-1][1].append(-d)
current=[1]
for i in range(n):
  b[i]=0
  dfs(a,i+1)
if success==0:
  print('No')
else:
  print('Yes')

Fixed submission:
visited=set()
success=1
import sys
sys.setrecursionlimit(1000000)
def dfs(graph, node):
  global visited
  global b
  global success
  if node not in visited:
    visited.add(node)
    for counter in range(len(graph[node-1][0])):
      if b[graph[node-1][0][counter]-1]==10000000000000000000:
        b[graph[node-1][0][counter]-1]=b[node-1]+graph[node-1][1][counter]
      else:
        if  b[graph[node-1][0][counter]-1]!=b[node-1]+graph[node-1][1][counter]:
          success=0
      dfs(graph, graph[node-1][0][counter])
      
n,m=map(int,input().split())
a=[]
b=[10000000000000000000]*n
for i in range(n):
  a.append([[],[]])
done=[0]*n
for i in range(m):
  l,r,d=map(int,input().split())
  a[l-1][0].append(r)
  a[l-1][1].append(d)
  a[r-1][0].append(l)
  a[r-1][1].append(-d)
current=[1]
for i in range(n):
  if i+1 in visited:
    continue
  b[i]=0
  dfs(a,i+1)
if success==0:
  print('No')
else:
  print('Yes')