Bzoj2002/洛谷P3203 [HNOI2010]弹飞绵羊（分块）

题面

Bzoj

洛谷

题解

大力分块，分块大小$\sqrt n$，对于每一个元素记一下跳多少次能跳到下一个块，以及跳到下一个块的哪个位置，修改的时候时候只需要更新元素所在的那一块即可，然后询问也是$\sqrt n$的模拟。

#include <cmath>
#include <cstdio>
#include <cstring>
#include <algorithm>
using std::min; using std::max;
using std::swap; using std::sort;
using std::__gcd;
typedef long long ll;

template<typename T>
void read(T &x) {
    int flag = 1; x = 0; char ch = getchar();
    while(ch < '0' || ch > '9') { if(ch == '-') flag = -flag; ch = getchar(); }
    while(ch >= '0' && ch <= '9') x = x * 10 + ch - '0', ch = getchar(); x *= flag;
}

const int N = 2e5 + 10, SN = 450, M = 1e5 + 10;
int n, m, k[N], x, y, siz, out[N], step[N];
int bel[N], l[SN], r[SN];

void doit (int L, int R) {
	for(int i = R; i >= L; --i) {
		int nxt = i + k[i];
		if(nxt > R) step[i] = 1, out[i] = nxt;
		else step[i] = step[nxt] + 1, out[i] = out[nxt];
	}
}

int main () {
#ifdef OFFLINE_JUDGE
    freopen("233.in", "r", stdin);
    freopen("233.out", "w", stdout);
#endif
	read(n), siz = sqrt(n);
	for(int i = 1; i <= n; ++i)
		read(k[i]), bel[i] = (i - 1) / siz + 1;
	for(int i = 1; i <= bel[n]; ++i) {
		l[i] = r[i - 1] + 1, r[i] = min(i * siz, n);
		doit(l[i], r[i]);
	}
	read(m); int opt;
	while(m--) {
		read(opt), read(x), ++x;
		if(opt == 1) {
			int ret = 0;
			while(x <= n) ret += step[x], x = out[x];
			printf("%d\n", ret);
		} else read(k[x]), doit(l[bel[x]], r[bel[x]]);
	}
	return 0;
}