People on a Line

http://icpc.upc.edu.cn/problem.php?id=6651 

#include<cstdio>
using namespace std;
int ff,f[500000],d[509000],n,m,x,y,z,i,j;
int find(int x) {
	if(f[x]==x)
		return x;
	int r=find(f[x]);
	d[x]=d[f[x]]+d[x];
	return f[x]=r;
}
int union1(int x,int y,int z) {
	int fx=find(x),fy=find(y);
	if(fx==fy)
		return z==d[y]-d[x];
	f[fy]=fx;
	d[fy]=d[x]+z-d[y];
	return 1;
}
int main() {
	scanf("%d%d",&n,&m);
	ff=1;
	for(i=1; i<=n; i++)
		f[i]=i;
	for(i=1; i<=m; i++) {
		scanf("%d%d%d",&x,&y,&z);
		if(ff)
			ff=union1(x,y,z);
	}
	if(ff)
		printf("Yes\n");
	else printf("No\n");
}