杭电hdu 3038 how many answers are wrong 并查集求解

http://acm.hdu.edu.cn/showproblem.php?pid=3038

经过网上的搜罗，基本上明白了这个题的意思，网站http://hi.baidu.com/fp_lv/blog/item/a471530a86df7b90d53f7c2c.html讲解的很清楚，我这里只记录下网址和我的代码，以便以后随时查看。

#include <stdio.h>
#define MAX 200001

int father[MAX];
int sum[MAX];//存储从1到i相加的结果

int n,m;
int ai, bi, si;

void init()
{
	for(int i = 0; i <= n; i ++){
		father[i] = i;
		sum[i] = 0;
	}
}

int getfather(int x)
{
	if(x == father[x])
		return x;
	int now = getfather(father[x]);//
	sum[x] += sum[father[x]];//需要我研究的地方
	father[x] = now;
	return now;
}

bool join(int a, int b)
{
	int fa = getfather(a);
	int fb = getfather(b);
	if(fa == fb)return false;
	father[fb] = fa;
	sum[fb] = sum[a] - sum[b] + si;//
	return true;
}

int main()
{
//	freopen("input.txt","r",stdin);
//	freopen("output.txt","w",stdout);
	
	while(~scanf("%d%d",&n,&m)){
		init();
		int ans = 0;
		while(m--){
			scanf("%d%d%d",&ai, &bi, &si);
			ai --;
			if(!join(ai, bi)&&sum[bi] - sum[ai] != si)ans ++;
		}
		printf("%d\n", ans);
	}
	return 0;
}