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# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System.Linq;
using System.Collections.Generic;
using System;

public class Info
{
    public int L { get; set; }
    public int r { get; set; }
    public int d { get; set; }
}

public class Hello
{
    public static void Main()
    {
        var q = new Queue<Info>();
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var m = int.Parse(line[1]);
        if (m == 0) { Console.WriteLine("Yes"); goto end; }
        var a = new long[n + 1];
        line = Console.ReadLine().Trim().Split(' ');
        var L = long.Parse(line[0]);
        var r = long.Parse(line[1]);
        var d = long.Parse(line[2]);
        a[L] = 1;
        a[r] = d + 1;
        for (int i = 1; i < m; i++)
        {
            line = Console.ReadLine().Trim().Split(' ');
            var wL = int.Parse(line[0]);
            var wr = int.Parse(line[1]);
            var wd = int.Parse(line[2]);
            if (a[wr] > 0 && a[wL] > 0 && a[wr] - a[wL] != wd) { Console.WriteLine("No"); goto end; }
            else if (a[wr] > 0 && a[wL] > 0 && a[wr] - a[wL] == wd) continue;
            else if (a[wr] == 0 && a[wL] > 0) a[wr] = wL + wd;
            else if (a[wL] == 0 && a[wr] > 0) a[wL] = wr - wd;
            else q.Enqueue(new Info { L = wL, r = wr, d = wd });
        }
        while (q.Count() > 0)
        {
            var x = q.Dequeue();
            var wL = x.L;
            var wr = x.r;
            var wd = x.d;
            if (a[wr] > 0 && a[wL] > 0 && a[wr] - a[wL] != wd) { Console.WriteLine("No"); goto end; }
            else if (a[wr] > 0 && a[wL] > 0 && a[wr] - a[wL] == wd) continue;
            else if (a[wr] == 0 && a[wL] > 0) a[wr] = wL + wd;
            else if (a[wL] == 0 && a[wr] > 0) a[wL] = wr - wd;
            else q.Enqueue(new Info { L = wL, r = wr, d = wd });
        }
        Console.WriteLine("Yes");
        end:;
    }
}