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 Go (1.6) (judge verdict: Wrong Answer)

package main

import "fmt"

var n, m, d, l, r int

const arraySize = 100001

var set = [arraySize]int{}
var a = [arraySize]int{}

func limit(x int) bool {
	return !(0 > x && x <= 1000000000)
}
func main() {
	fmt.Scanf("%d%d", &n, &m)

	for i := 0; i < m; i++ {
		fmt.Scanf("%d%d%d", &l, &r, &d)
		l--
		r--
		if set[l] == 0 && set[r] == 0 {
			val := a[l]
			a[r] = d + val
			set[l], set[r] = 1, 1
			if !limit(a[l]) || !limit(r) {
				fmt.Println("No")
				return
			}
		}
		if set[l] == 1 && set[r] == 1 {
			val := a[l]
			if a[r] != d+val {
				fmt.Println("No")
				return
			}
			if !limit(a[l]) || !limit(r) {
				fmt.Println("No")
				return
			}
		}
		if set[l] == 0 && set[r] == 1 {
			a[l] = a[r] - d
			set[l] = 1
			if !limit(a[l]) || !limit(r) {
				fmt.Println("No")
				return
			}
		}
		if set[l] == 1 && set[r] == 0 {
			a[r] = a[l] + d
			set[r] = 1
			if !limit(a[l]) || !limit(r) {
				fmt.Println("No")
				return
			}
		}
	}
	fmt.Println("Yes")
}