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 Ruby (2.3.3) (judge verdict: Accepted)

#from https://atcoder.jp/contests/abc087/submissions/4389032

class WeightedUnionFind
  def initialize(size)
    @rank = Array.new(size, 0)
    @parent = Array.new(size, &:itself)
    @weight = Array.new(size, 0)
  end
 
  def unite(id_x, id_y, w)
    cw = w + weight(id_x) - weight(id_y)
    x_parent = get_parent(id_x)
    y_parent = get_parent(id_y)
    return if x_parent == y_parent

    if @rank[x_parent] > @rank[y_parent]
      @weight[y_parent] = cw
      @parent[y_parent] = x_parent
    else
      @weight[x_parent] = -cw
      @parent[x_parent] = y_parent

      @rank[y_parent] += 1 if @rank[x_parent] == @rank[y_parent]
    end
  end

  def weight(idx)
    get_parent(idx)
    @weight[idx]
  end

  def weight_diff(x, y)
    weight(y)-weight(x)
  end

  def get_parent(id_x)
    if @parent[id_x] == id_x
      id_x
    else
      root = get_parent(@parent[id_x])
      @weight[id_x] += @weight[@parent[id_x]]
      @parent[id_x] = root
    end
  end

  def same_parent?(id_x, id_y)
    get_parent(id_x) == get_parent(id_y)
  end
end


n, m = gets.strip.split.map(&:to_i)
lrd = readlines.map {|line| line.split.map(&:to_i) }

wuf = WeightedUnionFind.new(n+1)

lrd.each do |l, r, d|
  if wuf.same_parent?(l,r)
    if wuf.weight_diff(l, r) != d
      puts 'No'
      exit
    end
  else
    wuf.unite(l, r, d)
  end
end

puts'Yes'