Buggy python submission (verdict: Runtime Error):
import heapq
n, m = map( int, input().split() )
adj_list = [ [] for i in range( n+1 ) ]
for _ in range( m ):
    a, b, c = map( int, input().split() )
    adj_list[ a ].append( ( b, c ) )
    adj_list[ b ].append( ( a, c ) )

# dijkstra
def dijkstra( start ):
    prev_node = [ -1 ] * ( n + 1 )
    INF = 10 ** 10
    VISITED = 1
    NOT_VISITED = 0
    cost = [ INF ] * ( n + 1 )
    cost[ start ] = 0
    visit = [ NOT_VISITED ] * ( n + 1 )
    queue = [ ( cost[ start ], start ) ]
    while len( queue ) > 0:
        c, v = heapq.heappop( queue )
        visit[ v ] = VISITED
        for u, cost_vu in adj_list[v]:
            if visit[ u ] == VISITED:
                continue
            if cost[u] > cost[v] + cost_vu:
                cost[u] = cost[v] + cost_vu
                heapq.heappush( queue, ( cost[u], u ) )
                prev_node[ u ] = v
    return prev_node

used_edge = [ [ False ] * ( m+1 ) for i in range( m+1 ) ]

used_count = 0
for s in range( 1, n+1 ):
    prev_node = dijkstra( s )
    for i in range( 1, n+1 ):
        j = prev_node[ i ]
        if j == -1:
            continue
        if used_edge[ i ][ j ] == False:
            used_count += 1
            used_edge[ i ][ j ] = True
            used_edge[ j ][ i ] = True

print( m - used_count )

Fixed submission:
import heapq
n, m = map( int, input().split() )
adj_list = [ [] for i in range( n+1 ) ]
for _ in range( m ):
    a, b, c = map( int, input().split() )
    adj_list[ a ].append( ( b, c ) )
    adj_list[ b ].append( ( a, c ) )

# dijkstra
def dijkstra( start ):
    prev_node = [ -1 ] * ( n + 1 )
    INF = 10 ** 10
    VISITED = 1
    NOT_VISITED = 0
    cost = [ INF ] * ( n + 1 )
    cost[ start ] = 0
    visit = [ NOT_VISITED ] * ( n + 1 )
    queue = [ ( cost[ start ], start ) ]
    while len( queue ) > 0:
        c, v = heapq.heappop( queue )
        visit[ v ] = VISITED
        for u, cost_vu in adj_list[v]:
            if visit[ u ] == VISITED:
                continue
            if cost[u] > cost[v] + cost_vu:
                cost[u] = cost[v] + cost_vu
                heapq.heappush( queue, ( cost[u], u ) )
                prev_node[ u ] = v
    return prev_node

used_edge = [ [ False ] * ( n+1 ) for i in range( n+1 ) ]

used_count = 0
for s in range( 1, n+1 ):
    prev_node = dijkstra( s )
    for i in range( 1, n+1 ):
        j = prev_node[ i ]
        if j == -1:
            continue
        if used_edge[ i ][ j ] == False:
            used_count += 1
            used_edge[ i ][ j ] = True
            used_edge[ j ][ i ] = True

print( m - used_count )

Buggy python submission (verdict: Runtime Error):
import heapq
n, m = map( int, input().split() )
adj_list = [ [] for i in range( n+1 ) ]
for _ in range( m ):
    a, b, c = map( int, input().split() )
    adj_list[ a ].append( ( b, c ) )
    adj_list[ b ].append( ( a, c ) )

# dijkstra
def dijkstra( start ):
    prev_node = [ -1 ] * ( n + 1 )
    INF = 10 ** 10
    VISITED = 1
    NOT_VISITED = 0
    cost = [ INF ] * ( n + 1 )
    cost[ start ] = 0
    visit = [ NOT_VISITED ] * ( n + 1 )
    queue = [ ( cost[ start ], start ) ]
    while len( queue ) > 0:
        c, v = heapq.heappop( queue )
        visit[ v ] = VISITED
        for u, cost_vu in adj_list[v]:
            if visit[ u ] == VISITED:
                continue
            if cost[u] > cost[v] + cost_vu:
                cost[u] = cost[v] + cost_vu
                heapq.heappush( queue, ( cost[u], u ) )
                prev_node[ u ] = v
    return prev_node

used_edge = [ [ False ] * ( m+1 ) for i in range( m+1 ) ]

used_count = 0
for s in range( 1, n+1 ):
    prev_node = dijkstra( s )
    for i in range( 1, m+1 ):
        j = prev_node[ i ]
        if j == -1:
            continue
        if used_edge[ i ][ j ] == False:
            used_count += 1
            used_edge[ i ][ j ] = True
            used_edge[ j ][ i ] = True

print( m - used_count )

Fixed submission:
import heapq
n, m = map( int, input().split() )
adj_list = [ [] for i in range( n+1 ) ]
for _ in range( m ):
    a, b, c = map( int, input().split() )
    adj_list[ a ].append( ( b, c ) )
    adj_list[ b ].append( ( a, c ) )

# dijkstra
def dijkstra( start ):
    prev_node = [ -1 ] * ( n + 1 )
    INF = 10 ** 10
    VISITED = 1
    NOT_VISITED = 0
    cost = [ INF ] * ( n + 1 )
    cost[ start ] = 0
    visit = [ NOT_VISITED ] * ( n + 1 )
    queue = [ ( cost[ start ], start ) ]
    while len( queue ) > 0:
        c, v = heapq.heappop( queue )
        visit[ v ] = VISITED
        for u, cost_vu in adj_list[v]:
            if visit[ u ] == VISITED:
                continue
            if cost[u] > cost[v] + cost_vu:
                cost[u] = cost[v] + cost_vu
                heapq.heappush( queue, ( cost[u], u ) )
                prev_node[ u ] = v
    return prev_node

used_edge = [ [ False ] * ( n+1 ) for i in range( n+1 ) ]

used_count = 0
for s in range( 1, n+1 ):
    prev_node = dijkstra( s )
    for i in range( 1, n+1 ):
        j = prev_node[ i ]
        if j == -1:
            continue
        if used_edge[ i ][ j ] == False:
            used_count += 1
            used_edge[ i ][ j ] = True
            used_edge[ j ][ i ] = True

print( m - used_count )

Buggy python submission (verdict: Runtime Error):
import heapq
n, m = map( int, input().split() )
adj_list = [ [] for i in range( 0, n+1 ) ]
for _ in range( m ):
    a, b, c = map( int, input().split() )
    adj_list[ a ].append( ( b, c ) )
    adj_list[ b ].append( ( a, c ) )

# dijkstra
def dijkstra( start ):
    prev_node = [ -1 ] * ( n + 1 )
    INF = 10 ** 10
    VISITED = 1
    NOT_VISITED = 0
    cost = [ INF ] * ( n + 1 )
    cost[ start ] = 0
    visit = [ NOT_VISITED ] * ( n + 1 )
    queue = [ ( cost[ start ], start ) ]
    while len( queue ) > 0:
        c, v = heapq.heappop( queue )
        visit[ v ] = VISITED
        for u, cost_vu in adj_list[v]:
            if visit[ u ] == VISITED:
                continue
            if cost[u] > cost[v] + cost_vu:
                cost[u] = cost[v] + cost_vu
                heapq.heappush( queue, ( cost[u], u ) )
                prev_node[ u ] = v
    return prev_node

used_edge = [ [ False ] * ( n+1 ) for i in range( n+1 ) ]

used_count = 0
for s in range( 1, n+1 ):
    prev_node = dijkstra( s )
    for i in range( 1, m+1 ):
        j = prev_node[ i ]
        if j == -1:
            continue
        if used_edge[ i ][ j ] == False:
            used_count += 1
            used_edge[ i ][ j ] = True
            used_edge[ j ][ i ] = True

print( m - used_count )

Fixed submission:
import heapq
n, m = map( int, input().split() )
adj_list = [ [] for i in range( n+1 ) ]
for _ in range( m ):
    a, b, c = map( int, input().split() )
    adj_list[ a ].append( ( b, c ) )
    adj_list[ b ].append( ( a, c ) )

# dijkstra
def dijkstra( start ):
    prev_node = [ -1 ] * ( n + 1 )
    INF = 10 ** 10
    VISITED = 1
    NOT_VISITED = 0
    cost = [ INF ] * ( n + 1 )
    cost[ start ] = 0
    visit = [ NOT_VISITED ] * ( n + 1 )
    queue = [ ( cost[ start ], start ) ]
    while len( queue ) > 0:
        c, v = heapq.heappop( queue )
        visit[ v ] = VISITED
        for u, cost_vu in adj_list[v]:
            if visit[ u ] == VISITED:
                continue
            if cost[u] > cost[v] + cost_vu:
                cost[u] = cost[v] + cost_vu
                heapq.heappush( queue, ( cost[u], u ) )
                prev_node[ u ] = v
    return prev_node

used_edge = [ [ False ] * ( n+1 ) for i in range( n+1 ) ]

used_count = 0
for s in range( 1, n+1 ):
    prev_node = dijkstra( s )
    for i in range( 1, n+1 ):
        j = prev_node[ i ]
        if j == -1:
            continue
        if used_edge[ i ][ j ] == False:
            used_count += 1
            used_edge[ i ][ j ] = True
            used_edge[ j ][ i ] = True

print( m - used_count )