Problem:
Joisino is planning to record N TV programs with recorders.  The TV can receive C channels numbered 1 through C.  The i-th program that she wants to record will be broadcast from time s_i to time t_i (including time s_i but not t_i) on Channel c_i.  Here, there will never be more than one program that are broadcast on the same channel at the same time.  When the recorder is recording a channel from time S to time T (including time S but not T), it cannot record other channels from time S-0.5 to time T (including time S-0.5 but not T).  Find the minimum number of recorders required to record the channels so that all the N programs are completely recorded.

Incorrect submission (verdict: Wrong Answer):
# using main() makes code faster from the point of view of "access to variables in global name-space"


# for i, a in enumerate(iterable)

# divmod(x, y) returns the tuple (x//y, x%y)
# manage median(s) using two heapq https://atcoder.jp/contests/abc127/tasks/abc127_f
import sys
sys.setrecursionlimit(10**7)
from itertools import accumulate, combinations, permutations # https://docs.python.org/ja/3/library/itertools.html
from math import factorial
def combinations_count(n, r):
    # faster than the following code
    
    #     return factorial(n) // (factorial(n - r) * factorial(r))
    if n - r < r: r = n - r
    if r == 0: return 1
    if r == 1: return n
    numerator = [n - r + k + 1 for k in range(r)]
    denominator = [k + 1 for k in range(r)]
    for p in range(2,r+1):
        pivot = denominator[p - 1]
        if pivot > 1:
            offset = (n - r) % p
            for k in range(p-1,r,p):
                numerator[k - offset] /= pivot
                denominator[k] /= pivot
    result = 1
    for k in range(r):
        if numerator[k] > 1:
            result *= int(numerator[k])
    return result
def combination_with_repetition_count(n, r):
    return combinations_count(n + r - 1, r)
from collections import deque, Counter # https://docs.python.org/ja/3/library/collections.html#collections.deque
from heapq import heapify, heappop, heappush, heappushpop, heapreplace,nlargest,nsmallest # https://docs.python.org/ja/3/library/heapq.html
from copy import deepcopy, copy # https://docs.python.org/ja/3/library/copy.html
from operator import itemgetter 
# ex1: List.sort(key=itemgetter(1))
# ex2: sorted(tuples, key=itemgetter(1,2))
from functools import reduce
from fractions import gcd # Deprecated since version 3.5: Use math.gcd() instead.
def gcds(numbers):
    return reduce(gcd, numbers)
def lcm(x, y):
    return (x * y) // gcd(x, y)
def lcms(numbers):
    return reduce(lcm, numbers, 1)

# first create factorial_list
# fac_list = mod_factorial_list(n)
INF = 10 ** 18
MOD = 10 ** 6 + 3
modpow = lambda a, n, p = MOD: pow(a, n, p) # Recursive function in python is slow!
def modinv(a, p = MOD):
    # evaluate reciprocal using Fermat's little theorem:
    # a**(p-1) is identical to 1 (mod p) when a and p is coprime
    return modpow(a, p-2, p)
def modinv_list(n, p = MOD):
    if n <= 1:
        return [0,1][:n+1]
    else:
        inv_t = [0,1]
        for i in range(2, n+1):
            inv_t += [inv_t[p % i] * (p - int(p / i)) % p]
        return inv_t
def modfactorial_list(n, p = MOD):
    if n == 0:
        return [1]
    else:
        l = [0] * (n+1)
        tmp = 1
        for i in range(1, n+1):
            tmp = tmp * i % p
            l[i] = tmp
        return l
def modcomb(n, k, fac_list = [], p = MOD):
    # fac_list = modfactorial_list(100)
    # print(modcomb(100, 5, modfactorial_list(100)))
    from math import factorial
    if n < 0 or k < 0 or n < k: return 0
    if n == 0 or k == 0: return 1
    if len(fac_list) <= n:
        a = factorial(n) % p
        b = factorial(k) % p
        c = factorial(n-k) % p
    else:
        a = fac_list[n]
        b = fac_list[k]
        c = fac_list[n-k]
    return (a * modpow(b, p-2, p) * modpow(c, p-2, p)) % p
def modadd(a, b, p = MOD):
    return (a + b) % MOD
def modsub(a, b, p = MOD):
    return (a - b) % p
def modmul(a, b, p = MOD):
    return ((a % p) * (b % p)) % p
def moddiv(a, b, p = MOD):
    return modmul(a, modpow(b, p-2, p))


# initialize variables and set inputs
#initialize variables
    # to initialize list, use [0] * n
    # to initialize two dimentional array, use [[0] * N for _ in range(N)]

    # open(0).read() is a convenient method:
    # ex) n, m, *x = map(int, open(0).read().split())
    #     min(x[::2]) - max(x[1::2])
    # ex2) *x, = map(int, open(0).read().split())
    #     don't forget to add comma after *x if only one variable is used
# calculate and output
    
    # ex1) print(*l) => when l = [2, 5, 6], printed 2 5 6


# sys.stdin = open('sample.txt') # for test

# functions used
r = lambda: sys.stdin.readline().strip() #single: int(r()), line: map(int, r().split())
R = lambda: list(map(int, r().split())) # line: R(), lines: [R() for _ in range(n)]
Rmap = lambda: map(int, r().split())

N, C = R()
STC = [R() for _ in range(N)]
tbl = [[0]*(2*(10**5)+5) for _ in range(C)]

# watch out: join tv programmes which are continuously broadcast in one channel
for s, t, c in STC:
    c -= 1
    if tbl[c][2*s] != 0:
        tbl[c][2*s] += 1
        tbl[c][2*t] -= 1
    elif tbl[c][2*t-1] != 0:
        tbl[c][2*t-1] -= 1
        tbl[c][2*s-1] += 1
    else:
        tbl[c][2*s-1] = 1
        tbl[c][2*t] = -1
# for s, t, c in STC:
#     c -= 1
#     if tbl[c][s] == -1:
#         tbl[c][s] = 0
#         tbl[c][t] = -1
#     elif tbl[c][t-1] == 1:
#         tbl[c][s-1] = 1
#         tbl[c][t-1] = 0
#     else:
#         tbl[c][s-1] = 1
#         tbl[c][t] = -1

tbl2 = [list(accumulate(a)) for a in tbl]
ans = max([sum(x) for x in zip(*tbl2)])
print(ans)



# res = 0

#     cc = 0
#     for j in range(C):
#         if tbl2[j][i]:
#             cc += 1
#     res = max(res, cc)
 
# print(res)

# if __name__ == '__main__':
#     main()

Fixed, accepted submission:
import sys
from itertools import accumulate

# functions used
r = lambda: sys.stdin.readline().strip() #single: int(r()), line: map(int, r().split())
R = lambda: list(map(int, r().split())) # line: R(), lines: [R() for _ in range(n)]
Rmap = lambda: map(int, r().split())

N, C = R()
STC = [R() for _ in range(N)]
#  0.5sec as one unit
tbl = [[0]*(2*(10**5)+5) for _ in range(C)]

for s, t, c in STC:
    c -= 1
    # if we can record the programms continuously (ver1)
    if tbl[c][2*s] != 0:
        tbl[c][2*s] += 1
        tbl[c][2*t] -= 1
    # if we can record the programms continuously (ver2)
    elif tbl[c][2*t-1] != 0:
        tbl[c][2*t-1] -= 1
        tbl[c][2*s-1] += 1
    # else:
    else:
        tbl[c][2*s-1] = 1
        tbl[c][2*t] = -1

tbl2 = [list(accumulate(a)) for a in tbl]

# ans = max([sum(x) for x in zip(*tbl2)])
# print(ans)

res = 0
for i in range(200002):
    cc = 0
    for j in range(C):
        if tbl2[j][i] == 1:
            cc += 1
    res = max(res, cc)
print(res)