分块

建图

1.

int Size, Num, L[Maxsn + 5], R[Maxsn + 5], Block[Maxn + 5];

void Build (int l, int r) {
	Size = sqrt (r - l + 1);
	Num = ceil ((r - l + 1) * 1.0 / Size);
	for (int i = 1; i < Num; i++) {
		L[i] = 1 + (i - 1) * Size;
		R[i] = i * Size;
		for (int j = L[i]; j <= R[i]; j++)
			Block[j] = i;
	}
	L[Num] = 1 + (Num - 1) * Size;
	R[Num] = r;
	for (int j = L[Num]; j <= R[Num]; j++)
		Block[j] = Num;
}

2.

#define l(x) (((x) - 1) * Size + 1)
#define r(x) (Min ((x) * Size, n))
#define Get(x) (((x) - 1) / Size + 1)