大概长这样：

bool cmp(node x, node y) return a[x].l < a[y].l
sort(a + 1, a + 1 + n, cmp)
for (int i = 1, R = m; i <= n; i++)
	if (a[i].l > R) ans++, R = a[i].r
	else R = min(R, a[i].r)