Problem:
Score : 800 points

Problem Statement

There are N squares arranged in a row.
The squares are numbered 1, 2, ..., N, from left to right.

Snuke is painting each square in red, green or blue.
According to his aesthetic sense, the following M conditions must all be satisfied.
The i-th condition is:

There are exactly x_i different colors among squares l_i, l_i + 1, ..., r_i.

In how many ways can the squares be painted to satisfy all the conditions?
Find the count modulo 10^9+7.

Constraints

1 ≤ N ≤ 300

1 ≤ M ≤ 300

1 ≤ l_i ≤ r_i ≤ N

1 ≤ x_i ≤ 3

Input

Input is given from Standard Input in the following format:

N M
l_1 r_1 x_1
l_2 r_2 x_2
:
l_M r_M x_M

Output

Print the number of ways to paint the squares to satisfy all the conditions, modulo 10^9+7.

Sample Input 1

3 1
1 3 3

Sample Output 1

6

The six ways are:

RGB

RBG

GRB

GBR

BRG

BGR

where R, G and B correspond to red, green and blue squares, respectively.

Sample Input 2

4 2
1 3 1
2 4 2

Sample Output 2

6

The six ways are:

RRRG

RRRB

GGGR

GGGB

BBBR

BBBG

Sample Input 3

1 3
1 1 1
1 1 2
1 1 3

Sample Output 3

0

There are zero ways.

Sample Input 4

8 10
2 6 2
5 5 1
3 5 2
4 7 3
4 4 1
2 3 1
7 7 1
1 5 2
1 7 3
3 4 2

Sample Output 4

108

Solution in Python (3.4.3) (judge verdict: Runtime Error)

from collections import defaultdict

MOD = 1000000007
iist = lambda: map(int,input().split())

N,M = iist()
Q = defaultdict(list)
for i in range(M):
  l,r,x = iist()
  Q[r].append((l,x))

if any(x != 1 for l,x in Q[1]):
  print(0)
  exit(0)

dp = defaultdict(int)
dp[0,0] = 3

x_sum = [3]
y_sum = [3]
s = 3

for pk in range(1,N):
  k = pk+1

  dp.update(((i,pk),s%MOD) for i,s in enumerate(map(sum, zip(x_sum,y_sum))))

  for i in range(pk):
    x_sum[i] += dp[i,pk]
  x_sum.append(0)
  y_sum.append((2*s)%MOD)
  s *= 3

  removes = [(i,j) for i,j in dp.keys()
            if any(x != (l<=i)+(l<=j)+1 for l,x in Q[k])]

  for i,j in removes:
    c = dp[i,j]
    del dp[i,j]
    x_sum[i] -= c
    y_sum[j] -= c
    s -= c

  for i,j in range(pk):
    x_sum[i] %= MOD
    y_sum[i] %= MOD
  s %= MOD

print(s)