在P3406中，我采用了scanf读取数据，导致答案错误，改为cin后答案正确。这是为什么？求大佬解释

int main()
{
	//scanf("%d%d", &n, &m);
	cin >> n >> m;
	for (int i = 1; i <= m; i++)
		//scanf("%d", &P[i]);
		cin >> P[i];
	for (int i = 1; i < n; i++)
		//scanf("%d%d%d", &a[i], &b[i],&c[i]);
		cin >> a[i] >> b[i] >> c[i];