SPOJ QTREE - Query on a tree

Posted 2020-06-17 Swm_sxt

Description

You are given a tree (an acyclic undirected connected graph) with N nodes, and edges numbered 1, 2, 3...N-1.

We will ask you to perfrom some instructions of the following form:

• CHANGE i ti : change the cost of the i-th edge to ti
  or
• QUERY a b : ask for the maximum edge cost on the path from node a to node b

Input

The first line of input contains an integer t, the number of test cases (t <= 20). t test cases follow.

For each test case:

• In the first line there is an integer N (N <= 10000),
• In the next N-1 lines, the i-th line describes the i-th edge: a line with three integers a b c denotes an edge between a, b of cost c (c<= 1000000),
• The next lines contain instructions "CHANGE i ti" or "QUERY a b",
• The end of each test case is signified by the string "DONE".

There is one blank line between successive tests.

Output

For each "QUERY" operation, write one integer representing its result.

Example

Input:
1

3
1 2 1
2 3 2
QUERY 1 2
CHANGE 1 3
QUERY 1 2
DONE

Output:
1
3


本来应该写树链剖分的，但既然要练LCT就敲敲咯……也是调了蛮久

#include<cstdio>
#include<cstring>
#include<algorithm>
#define MN 10010
using namespace std;

int p,ca,f;
inline int read(){
    p=0;ca=getchar();f=1;
    while(ca<‘0‘||ca>‘9‘) {if (ca==‘-‘) f=-1;ca=getchar();}
    while(ca>=‘0‘&&ca<=‘9‘) p=p*10+ca-48,ca=getchar();
    return p*f;
}
struct na{
    int y,ne,c,nu;
}b[MN*2];
int fa[MN],n,t,x,y,c,l[MN],r[MN],num,id[MN],key[MN],ch[MN][2],ma[MN];
bool rt[MN];
inline int max(int a,int b){return a>b?a:b;}
inline void update(int x){
    ma[x]=max(max(ma[ch[x][0]],ma[ch[x][1]]),key[x]);
}
inline void rot(int x){
    int y=fa[x],kind=ch[y][1]==x;
    fa[x]=fa[y];
    fa[y]=x;
    ch[y][kind]=ch[x][!kind];
    fa[ch[y][kind]]=y;
    ch[x][!kind]=y;
    if(rt[y]) rt[y]=0,rt[x]=1;else ch[fa[x]][ch[fa[x]][1]==y]=x;
    update(y);update(x);
}
inline void splay(int x){
    while(!rt[x]){
        if (rt[fa[x]]) rot(x);else
        if ((ch[fa[fa[x]]][1]==fa[x])==(ch[fa[x]][1]==x)) rot(fa[x]),rot(x);else rot(x),rot(x);
    }
}
inline void acc(int u){
    int x=0;
    while(u){
        splay(u);
        rt[ch[u][1]]=1;rt[ch[u][1]=x]=0;
        update(u);
        u=fa[x=u];
    }
}
inline void change(int x,int c){
    acc(x);
    key[x]=c;
    update(x);
}
inline void lca(int &u,int &v){
    acc(v);v=0;
    while(u){
        splay(u);
        if (!fa[u]) break;
        rt[ch[u][1]]=1;
        rt[ch[u][1]=v]=0;
        update(u);
        u=fa[v=u];
    }
}
inline int qu(int x,int y){
    lca(x,y);
    return max(ma[y],ma[ch[x][1]]);
}
inline void in(int x,int y,int c,int nu){
    num++;
    if (!l[x]) l[x]=num;else b[r[x]].ne=num;
    b[num].y=y;b[num].c=c;b[num].ne=0;b[num].nu=nu;r[x]=num;
}
inline void dfs(int x){
    for (int i=l[x];i;i=b[i].ne)
    if (!fa[b[i].y]){
        fa[b[i].y]=x;
        id[b[i].nu]=b[i].y;
        key[b[i].y]=b[i].c;
        dfs(b[i].y);
    }
}
char ss[10];
int main(){
    t=read();
    ma[0]=-1e9;
    while(t--){
        num=0;
        memset(rt,1,sizeof(rt));
        memset(fa,0,sizeof(fa));
        memset(ch,0,sizeof(ch));
        memset(l,0,sizeof(l));
        n=read();
        for (int i=1;i<n;i++){
            x=read();y=read();c=read();
            in(x,y,c,i);
            in(y,x,c,i);
        }
        fa[1]=-1;
        dfs(1);
        fa[1]=0;
        for(;;){
            scanf("%s",ss);
            if (ss[0]==‘D‘) break;
            x=read();y=read();
            if (ss[0]==‘Q‘) printf("%d\n",qu(x,y));else
            change(id[x],y);
        }
    }
}