ST表优化区间gcd
ST表的使用需要所求区间答案具有可重复性(询问时需要用到两个区间重叠来覆盖询问区间)
此题要求gcd为x的区间个数
可以用ST表处理出所有区间的\(gcd\) \(O(nlogn)\)
将区间的左端点\(l\)固定所有以 \(l\) 为左端点的区间\(gcd\)不超过\(log(n)\)个 及全部区间的\(gcd\)不超过\(nlogn\)种
证明:
以\(l\)为左端点\(r\)在向右扩的过程中此区间\((l,r)\)的\(gcd\)只会不变或减小(显然成立法)而每次减小必定是会少一个因子至少会除\(2\)所以最多也就\(log(n)\)个\(l\)的位置有\(n\)个所以所有区间就有\(nlogn\)种\(gcd\)
据此我们可以求出所有\(cnt[gcd_i]\)\((gcd\)为\(gcd_i\)的区间个数\()\)
当\(l\)固定时区间\(gcd\)的分布为一段一段的(\(gcd_1,gcd_2,gcd_3,...\))且具有二分性可以用二分找到\(gcd\)变化的位置从而求出\(gcd\)为\(gcd_i\)的区间个数累加到\(cnt[gcd_i]\)中
最后询问直接输出\(cnt[x]\)即可
CGCDSSQ
题面翻译
给出一个长度为\(n(1<=n<=10^{5})\) 的序列和\(q(1<=q<=3*10^{5})\) 个询问,每个询问输出一行,询问\(gcd(a_l,a_{l+1},...,a_r)=x\) 的\((i,j)\) 的对数.
感谢@凌幽 提供的翻译
题目描述
Given a sequence of integers $ a_{1},...,a_{n} $ and $ q $ queries $ x_{1},...,x_{q} $ on it. For each query $ x_{i} $ you have to count the number of pairs $ (l,r) $ such that $ 1<=l<=r<=n $ and $ gcd(a_{l},a_{l+1},...,a_{r})=x_{i} $ .
is a greatest common divisor of $ v_{1},v_{2},...,v_{n} $ , that is equal to a largest positive integer that divides all $ v_{i} $ .
输入格式
Given a sequence of integers $ a_{1},...,a_{n} $ and $ q $ queries $ x_{1},...,x_{q} $ on it. For each query $ x_{i} $ you have to count the number of pairs $ (l,r) $ such that $ 1<=l<=r<=n $ and $ gcd(a_{l},a_{l+1},...,a_{r})=x_{i} $ .
is a greatest common divisor of $ v_{1},v_{2},...,v_{n} $ , that is equal to a largest positive integer that divides all $ v_{i} $ .
输出格式
For each query print the result in a separate line.
样例 #1
样例输入 #1
3
2 6 3
5
1
2
3
4
6
样例输出 #1
1
2
2
0
1
样例 #2
样例输入 #2
7
10 20 3 15 1000 60 16
10
1
2
3
4
5
6
10
20
60
1000
样例输出 #2
14
0
2
2
2
0
2
2
1
1
std
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define il inline
#define re register
const int N = 1e5+9;
int n,m,f[N][25];
map<int,ll>cnt;
il int gcd(re int x,re int y)
{
while(y)
{
x%=y;
swap(x,y);
}
return x;
}
il init()
{
for(re int j = 1;j <= 23;j++)
for(re int i = 1;i+(1<<j)-1 <= n;i++)
f[i][j] = gcd(f[i][j-1],f[i+(1<<(j-1))][j-1]);
}
il int query(int l,int r)
{
re int k = log2(r-l+1);
return gcd(f[l][k],f[r-(1<<k)+1][k]);
}
int main()
{
scanf("%d",&n);
for(re int i = 1;i <= n;i++)scanf("%d",&f[i][0]);
init();
for(re int i = 1;i <= n;i++)
{
re int L = i;
while(L <= n)
{
re int st = query(i,L);
int l = L,r = n+1;
while(l < r)
{
int mid = (l+r)>>1;
if(query(i,mid) != st)r = mid;
else l = mid+1;
}
cnt[st] += l-L;
L = l;
}
}
scanf("%d",&m);
while(m--)
{
re int x;
scanf("%d",&x);
printf("%lld\n",cnt[x]);
}
return 0;
}
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