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 PyPy3 (2.4.0) (judge verdict: Accepted)

import sys
from collections import deque

def solve():
    input = sys.stdin.readline
    N, M = map(int, input().split())
    E = [[] for _ in range(N)]
    for _ in range(M):
        l, r, d = map(int, input().split())
        E[l-1].append((r - 1, d))
        E[r-1].append((l - 1, -d))
    Pos = [10 ** 20] * N
    q = deque()
    flag = True
    for i in range(N):
        if Pos[i] == 10 ** 20:
            q.append((i, 0))
            minX, maxX = 0, 0
            while q:
                x, p = q.popleft()
                if Pos[x] == 10 ** 20:
                    minX = min(minX, p)
                    maxX = max(maxX, p)
                    Pos[x] = p
                    for ne, d in E[x]: q.append((ne, p + d))
                elif Pos[x] == p: continue
                else:
                    flag = False
                    break
            else:
                if maxX - minX <= 10 ** 9: continue
                else: flag = False
            if not flag:
                print("No")
                break
    else: print("Yes")
    #print(Pos)
            
    return 0

if __name__ == "__main__":
    solve()