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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iomanip>
#define inf 2147483647
using namespace std;
struct info
{
    int l,r,d;
}s[200005];
int n,m;
int flag = 1;
int p[100005];
bool cmp(info a,info b)
{
    return a.l < b.l;
}
int main()
{
    cin>>n>>m;
    for(int i = 1;i <= n;i ++)
        s[i].d = inf;
    for(int i = 0;i < m;i ++)
    {
        cin>>s[i].l>>s[i].r>>s[i].d;
        if(s[i].l > s[i].r)
        {
            int t = s[i].l;
            s[i].l = s[i].r;
            s[i].r = t;
            s[i].d = -s[i].d;
        }
    }
    sort(s,s + m,cmp);
    p[s[0].l] = 0;
    for(int i = 0;i < m;i ++)
    {
        if(p[s[i].l] == inf && p[s[i].r] == inf)
        {
            if(i == m - 1)break;
            else s[m ++] = s[i];
        }
        else if(p[s[i].l] == inf)p[s[i].l] = p[s[i].r] - s[i].d;
        else if(p[s[i].r] == inf)p[s[i].r] = p[s[i].l] + s[i].d;
        else
        {
            if(p[s[i].r] - p[s[i].l] != s[i].d)
            {
                flag = 0;
                break;
            }
        }
    }
    if(flag)cout<<"Yes";
    else cout<<"No";
}