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 C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>

int p[100001];
long dis[100001]={};

int dfs(int x){
  if(p[x]==x)
    return x;
  return dfs(p[x]);
}

long kyori(int x,long k){
  if(p[x]==x)
    return k;
  return kyori(p[x],dis[x]+k);
}

int main(){
  int n,m,i,l,r,x,y;
  long d,d1,d2;
  scanf("%d %d",&n,&m);
  for(i-0;i<n+1;i++)
    p[i]=i;
  for(i=0;i<m;i++){
    scanf("%d %d %ld",&l,&r,&d);
    x=dfs(l);
    y=dfs(r);
    d1=kyori(l,0);
    d2=kyori(r,0);
    p[l]=x;
    p[r]=y;
    dis[l]=d1;
    dis[r]=d2;
    if(x!=y){
      p[x]=y;
      dis[x]=d+kyori(r,0)-kyori(l,0);
    }
    else{
      if(d-d1+d2!=0){
        printf("No\n");
        return 0;
      }
    }
  }
  printf("Yes\n");
}