CF 題目集錦 PART 7 #264 div 2 E
【原題】
E. Caisa and Tree time limit per test 10 seconds memory limit per test 256 megabytes input standard input output standard outputCaisa is now at home and his son has a simple task for him.
Given a rooted tree with n vertices, numbered from 1 to n (vertex 1 is
the root). Each vertex of the tree has a value. You should answer q
-
Format of the query is "1 v". Let's write out the sequence of vertices along the path from the root to vertex v: u1, u2, ..., uk (u1 = 1; uk = v).
You need to output such a vertex ui that gcd(value of ui, value of v) > 1 and i < k.
If there are several possible vertices u
- Format of the query is "2 v w". You must change the value of vertex v to w.
You are given all the queries, help Caisa to solve the problem.
Input
The first line contains two space-separated integers n, q (1 ≤ n, q ≤ 105
The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 2·106), where ai represent the value of node i.
Each of the next n - 1 lines contains two integers xi and yi (1 ≤ xi, yi ≤ n; xi ≠ yi), denoting the edge of the tree between vertices xi and yi.
Each of the next q lines contains a query in the format that is given above. For each query the following inequalities hold: 1 ≤ v ≤ n and 1 ≤ w ≤ 2·106. Note that: there are no more than 50 queries that changes the value of a vertex.
OutputFor each query of the first type output the result of the query.
Sample test(s) input4 6 10 8 4 3 1 2 2 3 3 4 1 1 1 2 1 3 1 4 2 1 9 1 4output
-1 1 2 -1 1Note
gcd(x, y) is greatest common divisor of two integers x and y.
【分析】這道題是做現場賽的。本來能A的,但是太緊張了=而且也不會用vector,邊表搞的麻煩死了。
開始看到修改操作才50次、時間又鬆,真是爽!估計每次可以暴力重構這顆樹,然後對於每個質因子記錄最優值。
首先每次不能sqrt的效率列舉一個數的因子,我們可以預處理出每個數的所有質因子。(其實有更省空間的)
剩下來要解決的問題是:因為我是用dfs的,怎麼把某個子樹的資訊在搜完後再去掉?(以免影響其他子樹)HHD表示用vector一點也不虛。其實應該也可以用邊表類似的思路,但是麻煩= =
【程式碼】
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<vector>
#define N 100005
#define S 2000005
#define push push_back
#define pop pop_back
using namespace std;
vector<int>fac[S],f[S];
int data[N],ans[N],end[N],pf[S],deep[N];
int C,cnt,n,Q,i,x,y,opt;
struct arr{int go,next;}a[N*2];
inline void add(int u,int v){a[++cnt].go=v;a[cnt].next=end[u];end[u]=cnt;}
inline void init()
{
int H=2000000;
for (int i=2;i<=H;i++)
if (!pf[i])
{
for (int j=i;j<=H;j+=i)
fac[j].push(i),pf[j]=1;
}
}
void dfs(int k,int fa)
{
int P=data[k];
for (int i=0;i<fac[P].size();i++)
{
int go=fac[P][i],temp=f[go].size();
if (temp&&deep[f[go][temp-1]]>deep[ans[k]]) ans[k]=f[go][temp-1];
f[go].push(k);
}
for (int i=end[k];i;i=a[i].next)
if (a[i].go!=fa)
dfs(a[i].go,k);
for (int i=0;i<fac[P].size();i++)
f[fac[P][i]].pop();
}
inline void get_deep(int k,int fa)
{
for (int i=end[k];i;i=a[i].next)
if (a[i].go!=fa) deep[a[i].go]=deep[k]+1,get_deep(a[i].go,k);
}
int main()
{
scanf("%d%d",&n,&Q);
for (i=1;i<=n;i++)
scanf("%d",&data[i]);
for (i=1;i<n;i++)
scanf("%d%d",&x,&y),add(x,y),add(y,x);
init();deep[0]=-1;get_deep(1,0);
memset(ans,0,sizeof(ans));dfs(1,0);
while (Q--)
{
scanf("%d%d",&opt,&x);
if (opt==1) {printf("%d\n",ans[x]?ans[x]:-1);continue;}
memset(ans,0,sizeof(ans));
scanf("%d",&y);data[x]=y;dfs(1,0);
}
return 0;
}