Buggy python submission (verdict: Runtime Error):
N = int(input())

adj = [[] for i in range(N)]
for i in range(N - 1):
    a, b, c = map(int, input().split())
    adj[-a].append((b, c))
    adj[-b].append((a, c))

Q, K = map(int, input().split())
query = [tuple(map(int, input().split())) for i in range(Q)]

# dist[-i]:頂点Kから頂点iまでの距離
dist = [0 for i in range(N)]

def dfs(v, prv, ds):
    dist[-v] = ds
    for nxt, c in adj[-v]:
        if nxt != prv:
            dfs(nxt, v, ds + c)

dfs(K, None, 0)

for x, y in query:
    print(dist[-x] + dist[-y])


Fixed submission:
import sys
sys.setrecursionlimit(1000000)

N = int(input())

adj = [[] for i in range(N)]
for i in range(N - 1):
    a, b, c = map(int, input().split())
    adj[-a].append((b, c))
    adj[-b].append((a, c))

Q, K = map(int, input().split())
query = [tuple(map(int, input().split())) for i in range(Q)]

# dist[-i]:頂点Kから頂点iまでの距離
dist = [0 for i in range(N)]

def dfs(v, prv, ds):
    dist[-v] = ds
    for nxt, c in adj[-v]:
        if nxt != prv:
            dfs(nxt, v, ds + c)

dfs(K, None, 0)

for x, y in query:
    print(dist[-x] + dist[-y])

Buggy python submission (verdict: Runtime Error):
N = int(input())

adj = [set() for i in range(N)]
for i in range(N - 1):
    a, b, c = map(int, input().split())
    adj[-a].add((b, c))
    adj[-b].add((a, c))

Q, K = map(int, input().split())
query = [tuple(map(int, input().split())) for i in range(Q)]

# dist[-i]:頂点Kから頂点iまでの距離
dist = [0 for i in range(N)]

def dfs(v, prv, ds):
    dist[-v] = ds
    for nxt, c in adj[-v]:
        if nxt != prv:
            dfs(nxt, v, ds + c)

dfs(K, None, 0)

for x, y in query:
    print(dist[-x] + dist[-y])


Fixed submission:
import sys
sys.setrecursionlimit(1000000)

N = int(input())

adj = [[] for i in range(N)]
for i in range(N - 1):
    a, b, c = map(int, input().split())
    adj[-a].append((b, c))
    adj[-b].append((a, c))

Q, K = map(int, input().split())
query = [tuple(map(int, input().split())) for i in range(Q)]

# dist[-i]:頂点Kから頂点iまでの距離
dist = [0 for i in range(N)]

def dfs(v, prv, ds):
    dist[-v] = ds
    for nxt, c in adj[-v]:
        if nxt != prv:
            dfs(nxt, v, ds + c)

dfs(K, None, 0)

for x, y in query:
    print(dist[-x] + dist[-y])

Buggy python submission (verdict: Time Limit Exceeded):
N = int(input())
edge = set(tuple(map(int, input().split())) for i in range(N-1))
Q, K = map(int, input().split())
query = [tuple(map(int, input().split())) for i in range(Q)]

# dist[-i]:頂点Kから頂点iまでの距離
dist = [None for i in range(N)]
dist[-K] = 0
while edge:
    rm = set()
    for a, b, c in edge:
        if dist[-a] is not None:
            dist[-b] = dist[-a] + c
            rm.add((a, b, c))
        elif dist[-b] is not None:
            dist[-a] = dist[-b] + c
            rm.add((a, b, c))
    edge -= rm

for x, y in query:
    print(dist[-x] + dist[-y])


Fixed submission:
import sys
sys.setrecursionlimit(1000000)

N = int(input())

adj = [[] for i in range(N)]
for i in range(N - 1):
    a, b, c = map(int, input().split())
    adj[-a].append((b, c))
    adj[-b].append((a, c))

Q, K = map(int, input().split())
query = [tuple(map(int, input().split())) for i in range(Q)]

# dist[-i]:頂点Kから頂点iまでの距離
dist = [0 for i in range(N)]

def dfs(v, prv, ds):
    dist[-v] = ds
    for nxt, c in adj[-v]:
        if nxt != prv:
            dfs(nxt, v, ds + c)

dfs(K, None, 0)

for x, y in query:
    print(dist[-x] + dist[-y])