Problem p02887 (python)

Fixed submission:
# -*- coding: utf-8 -*-
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub

sys.setrecursionlimit(100000)
input = sys.stdin.readline


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


@mt
def slv(N, S):
    ans = 1
    for i in range(0, N-1):
        if S[i] != S[i+1]:
            ans += 1

    return ans


def main():
    N = read_int()
    S = read_str()
    print(slv(N, S))


if __name__ == '__main__':
    main()

Buggy submission (verdict: Runtime Error):

# -*- coding: utf-8 -*-
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub

sys.setrecursionlimit(100000)
input = sys.stdin.readline


def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


@mt
def slv(N, M, L, ABC, Q, ST):

    g = defaultdict(dict)
    for a, b, c in ABC:
        g[a][b] = c
        g[b][a] = c
    
    dd = defaultdict(lambda: -1)
    def f(s, t):
        if (s, t) in dd:
            return dd[(s, t)]
        q = [(0, s)]
        done = set([s])
        d = 0
        while q:
            d, u = heapq.heappop(q)
            if u in done:
                continue
            qq = [(-L, u)]
            cand = set()
            while qq:
                rem, uu = heapq.heappop(qq)
                rem = -rem
                for vv in g[uu]:
                    if rem-g[uu][vv] < 0:
                        continue
                    if vv in done:
                        continue
                    qq.append((-(rem-g[uu][vv]), vv))
                    cand.add(vv)
            
            done |= cand
            for v in cand:
                dd[(s, v)] = d
                heapq.heappush(q, (d+1, v))

        for i in range(1, N+1):
            if i not in done:
                dd[(s, i)] = -1

        return dd[(s, t)]

    for s, t in ST:
        print(f(s, t))



def main():
    N, M, L = read_int_n()
    ABC = [read_int_n() for _ in range(M)]
    Q = read_int()
    ST = [read_int_n() for _ in range(Q)]
    (slv(N, M, L, ABC, Q, ST))


if __name__ == '__main__':
    main()