Problem:
Score : 400 points

Problem Statement

There are N people standing on the x-axis.
Let the coordinate of Person i be x_i.
For every i, x_i is an integer between 0 and 10^9 (inclusive).
It is possible that more than one person is standing at the same coordinate.

You will given M pieces of information regarding the positions of these people.
The i-th piece of information has the form (L_i, R_i, D_i).
This means that Person R_i is to the right of Person L_i by D_i units of distance, that is, x_{R_i} - x_{L_i} = D_i holds.

It turns out that some of these M pieces of information may be incorrect.
Determine if there exists a set of values (x_1, x_2, ..., x_N) that is consistent with the given pieces of information.

Constraints

1 \leq N \leq 100 000

0 \leq M \leq 200 000

1 \leq L_i, R_i \leq N (1 \leq i \leq M)

0 \leq D_i \leq 10 000 (1 \leq i \leq M)

L_i \neq R_i (1 \leq i \leq M)

If i \neq j, then (L_i, R_i) \neq (L_j, R_j) and (L_i, R_i) \neq (R_j, L_j).

D_i are integers.

Input

Input is given from Standard Input in the following format:

N M
L_1 R_1 D_1
L_2 R_2 D_2
:
L_M R_M D_M

Output

If there exists a set of values (x_1, x_2, ..., x_N) that is consistent with all given pieces of information, print Yes; if it does not exist, print No.

Sample Input 1

3 3
1 2 1
2 3 1
1 3 2

Sample Output 1

Yes

Some possible sets of values (x_1, x_2, x_3) are (0, 1, 2) and (101, 102, 103).

Sample Input 2

3 3
1 2 1
2 3 1
1 3 5

Sample Output 2

No

If the first two pieces of information are correct, x_3 - x_1 = 2 holds, which is contradictory to the last piece of information.

Sample Input 3

4 3
2 1 1
2 3 5
3 4 2

Sample Output 3

Yes

Sample Input 4

10 3
8 7 100
7 9 100
9 8 100

Sample Output 4

No

Sample Input 5

100 0

Sample Output 5

Yes

Solution in Python (3.4.3) (judge verdict: Accepted)

N,M=map(int,input().split())

parent = [i for i in range(N+1)]
distance = [0 for i in range(N+1)]
depth = [1 for i in range(N+1)]

def root(x):
    if x == parent[x]:
        return x
    else:
        return root(parent[x])

def to_root(x):
    if x == parent[x]:
        return 0
    else:
        return distance[x] + to_root(parent[x])

for _ in range(M):
    L, R, D = map(int, input().split())
    # print("distance", D, to_root(L), to_root(R))
    # print("root    ", root(L), root(R))
    # print(_, L, R, D)
    if root(L) == root(R):
        l = to_root(L)
        r = to_root(R)
        # print("distance", D, l, r)
        # print("root    ", root(L), root(R))
        if D != r-l:
            # print(parent)
            # print(distance)
            print("No")
            exit()
    else:
        rootL = root(L)
        rootR = root(R)
        if depth[rootL] < depth[rootR]:
            L,R = R,L
            D = -D
        rootL = root(L)
        rootR = root(R)
        parent[rootR] = rootL
        distance[rootR] = -to_root(R)+to_root(L)+D
        depth[rootL] = max(rootL, depth[rootR]+1)
print("Yes")