Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin, setrecursionlimit
import collections


def initialize_cmb(m, mod=10 ** 9 + 7):
    fac = [0] * m
    finv = [0] * m
    inv = [0] * m
    fac[0] = 1
    finv[0] = 1
    if m > 1:
        fac[1] = 1
        finv[1] = 1
        inv[1] = 1
        for i in range(2, m):
            fac[i] = fac[i-1] * i % mod
            inv[i] = mod - inv[mod % i] * (mod // i) % mod
            finv[i] = finv[i - 1] * inv[i] % mod
    return fac, finv


def cmb(n, k, fac, finv, mod=10 ** 9 + 7):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n - k] % mod) % mod


def main():
    input = stdin.readline
    s = list(input()[:-1])
    s = list(map(int, s))
    N = len(s)
    mod = [0] * N
    mod[-1] = s[-1] % 2019
    for i in reversed(range(N - 1)):
        mod[i] = (mod[i + 1] + s[i] * 10 ** (N - i - 1)) % 2019

    fac, finv = initialize_cmb(N)

    counter = collections.Counter(mod)

    ans = 0

    for k, v in counter.items():
        if k == 0:
            ans += v
        elif v > 1:
            ans += cmb(v, 2, fac, finv)

    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()


Fixed submission:
from sys import stdin, setrecursionlimit


def main():
    input = stdin.readline
    s = list(input()[:-1])[::-1]
    N = len(s)
    p10 = [1]
    tmp = 1
    for _ in range(N - 1):
        tmp = tmp * 10 % 2019
        p10.append(tmp)
    mod = []
    tmp = 0
    for num, p in zip(s, p10):
        tmp = (tmp + int(num) * p) % 2019
        mod.append(tmp)

    mod.sort()
    mod.insert(0, 0)

    ans = 0
    count = 1
    for i in range(1, N + 1):
        if mod[i] == mod[i - 1]:
            count += 1
        else:
            ans += count * (count - 1) // 2
            count = 1
    ans += count * (count - 1) // 2
    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin, setrecursionlimit
import collections


def initialize_cmb(m, mod=10 ** 9 + 7):
    fac = [0] * m
    finv = [0] * m
    inv = [0] * m
    fac[0] = 1
    finv[0] = 1
    if m > 1:
        fac[1] = 1
        finv[1] = 1
        inv[1] = 1
        for i in range(2, m):
            fac[i] = fac[i-1] * i % mod
            inv[i] = mod - inv[mod % i] * (mod // i) % mod
            finv[i] = finv[i - 1] * inv[i] % mod
    return fac, finv


def cmb(n, k, fac, finv, mod=10 ** 9 + 7):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n - k] % mod) % mod


def main():
    input = stdin.readline
    s = list(input()[:-1])
    s = list(map(int, s))
    N = len(s)
    mod = [0] * N
    mod[-1] = s[-1] % 2019
    for i in reversed(range(N - 1)):
        mod[i] = (mod[i + 1] + s[i] * 10 ** (N - i - 1)) % 2019

    fac, finv = initialize_cmb(N)

    counter = collections.Counter(mod)

    ans = 0

    for k, v in counter.items():
        if k == 0:
            ans += v
        elif v > 1:
            ans += cmb(v, 2, fac, finv)

    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()


Fixed submission:
from sys import stdin, setrecursionlimit


def main():
    input = stdin.readline
    s = list(input()[:-1])[::-1]
    N = len(s)
    p10 = [1]
    tmp = 1
    for _ in range(N - 1):
        tmp = tmp * 10 % 2019
        p10.append(tmp)
    mod = []
    tmp = 0
    for num, p in zip(s, p10):
        tmp = (tmp + int(num) * p) % 2019
        mod.append(tmp)

    mod.sort()
    mod.insert(0, 0)

    ans = 0
    count = 1
    for i in range(1, N + 1):
        if mod[i] == mod[i - 1]:
            count += 1
        else:
            ans += count * (count - 1) // 2
            count = 1
    ans += count * (count - 1) // 2
    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin, setrecursionlimit
import collections


def initialize_cmb(m, mod=10 ** 9 + 7):
    fac = [0] * m
    finv = [0] * m
    inv = [0] * m
    fac[0] = 1
    finv[0] = 1
    if m > 1:
        fac[1] = 1
        finv[1] = 1
        inv[1] = 1
        for i in range(2, m):
            fac[i] = fac[i-1] * i % mod
            inv[i] = mod - inv[mod % i] * (mod // i) % mod
            finv[i] = finv[i - 1] * inv[i] % mod
    return fac, finv


def cmb(n, k, fac, finv, mod=10 ** 9 + 7):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n - k] % mod) % mod


def main():
    input = stdin.buffer.readline
    s = input()[:-1].decode()
    N = len(s)
    mod = [0] * N
    for i in range(N):
        mod[i] = int(s[i:N]) % 2019

    fac, finv = initialize_cmb(N)

    counter = collections.Counter(mod)

    ans = 0

    for k, v in counter.items():
        if k == 0:
            ans += v
        elif v > 1:
            ans += cmb(v, 2, fac, finv)

    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()


Fixed submission:
from sys import stdin, setrecursionlimit


def main():
    input = stdin.readline
    s = list(input()[:-1])[::-1]
    N = len(s)
    p10 = [1]
    tmp = 1
    for _ in range(N - 1):
        tmp = tmp * 10 % 2019
        p10.append(tmp)
    mod = []
    tmp = 0
    for num, p in zip(s, p10):
        tmp = (tmp + int(num) * p) % 2019
        mod.append(tmp)

    mod.sort()
    mod.insert(0, 0)

    ans = 0
    count = 1
    for i in range(1, N + 1):
        if mod[i] == mod[i - 1]:
            count += 1
        else:
            ans += count * (count - 1) // 2
            count = 1
    ans += count * (count - 1) // 2
    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin, setrecursionlimit


def initialize_cmb(m, mod=10 ** 9 + 7):
    fac = [0] * m
    finv = [0] * m
    inv = [0] * m
    fac[0] = 1
    finv[0] = 1
    if m > 1:
        fac[1] = 1
        finv[1] = 1
        inv[1] = 1
        for i in range(2, m):
            fac[i] = fac[i-1] * i % mod
            inv[i] = mod - inv[mod % i] * (mod // i) % mod
            finv[i] = finv[i - 1] * inv[i] % mod
    return fac, finv


def cmb(n, k, fac, finv, mod=10 ** 9 + 7):
    if n < k:
        return 0
    if n < 0 or k < 0:
        return 0
    return fac[n] * (finv[k] * finv[n - k] % mod) % mod


def main():
    input = stdin.buffer.readline
    s = input()[:-1].decode()
    N = len(s)
    mod = [0] * N
    for i in range(N):
        mod[i] = int(s[i:N]) % 2019

    fac, finv = initialize_cmb(N)

    ans = mod.count(0)

    for i in range(2019):
        ans += cmb(mod.count(i), 2, fac, finv)

    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()


Fixed submission:
from sys import stdin, setrecursionlimit


def main():
    input = stdin.readline
    s = list(input()[:-1])[::-1]
    N = len(s)
    p10 = [1]
    tmp = 1
    for _ in range(N - 1):
        tmp = tmp * 10 % 2019
        p10.append(tmp)
    mod = []
    tmp = 0
    for num, p in zip(s, p10):
        tmp = (tmp + int(num) * p) % 2019
        mod.append(tmp)

    mod.sort()
    mod.insert(0, 0)

    ans = 0
    count = 1
    for i in range(1, N + 1):
        if mod[i] == mod[i - 1]:
            count += 1
        else:
            ans += count * (count - 1) // 2
            count = 1
    ans += count * (count - 1) // 2
    print(ans)


if __name__ == "__main__":
    setrecursionlimit(10000)
    main()