Snacks

Snacks

题目链接：http://acm.split.hdu.edu.cn/showproblem.php?pid=5692

dfs序+线段树

这道题涉及到对整棵树的值修改，考虑将树状结构用dfs序转化成线性结构，将树的修改转化为区间修改以降低时间复杂度（之前组队赛的时候遇到一道类似的没调出来...代码能力太缺乏了...）

代码如下：

 #include<cstdio>
 #include<vector>
 #include<iostream>
 #include<cstring>
 #pragma comment(linker, "/STACK:1024000000,1024000000")
 #define LL long long
 #define N 100100
 #define lson (x<<1)
 #define rson (x<<1|1)
 #define mid ((l+r)>>1)
 using namespace std;
 struct node{
     LL sum,lazy;
 }a[N<<];
 LL val[N];
 int L[N],R[N];
 LL spre[N];
 int index;
 bool vis[N];
 vector<int>e[N];
 void init(){
     //for(int i=0;i<N;++i)e[i].clear();
     //memset(a,0,sizeof(a));
     memset(vis,,sizeof(vis));
     memset(L,,sizeof(L));
     memset(R,,sizeof(R));
     memset(val,,sizeof(val));
     memset(spre,,sizeof(spre));
     index=;
 }
 void dfs(int num,LL v){
     vis[num]=;
     ++index;
     L[num]=index;
     for(LL i=;i<e[num].size();i++)
         if(!vis[e[num][i]])dfs(e[num][i],v+val[e[num][i]]);
     e[num].clear();
     spre[L[num]]=v;
     R[num]=index;
 }
 void push_up(int x){
     a[x].sum=max(a[lson].sum,a[rson].sum);
 }
 void push_down(int x){
     a[rson].sum+=a[x].lazy;
     a[rson].lazy+=a[x].lazy;
     a[lson].sum+=a[x].lazy;
     a[lson].lazy+=a[x].lazy;
     a[x].lazy=;
 }
 void build(int x,int l,int r){
     a[x].lazy=a[x].sum=;
     if(l==r){
         a[x].sum=spre[l];
         return;
     }
     build(lson,l,mid);
     build(rson,mid+,r);
     push_up(x);
 }
 void add(int x,int l,int r,int cl,int cr,LL v){
     if(cl<=l&&r<=cr){
         a[x].sum+=v;
         a[x].lazy+=v;
         return;
     }
     if(a[x].lazy!=)push_down(x);/**except this!!!**/
     if(cl<=mid)add(lson,l,mid,cl,cr,v);
     if(mid<cr)add(rson,mid+,r,cl,cr,v);
     push_up(x);
 }
 LL query(int x,int l,int r,int ql,int qr){
     if(ql<=l&&r<=qr)return a[x].sum;
     if(a[x].lazy!=)push_down(x);
     LL temp=-(LL);
     if(ql<=mid)temp=max(temp,query(lson,l,mid,ql,qr));
     if(mid<qr)temp=max(temp,query(rson,mid+,r,ql,qr));
     return temp;
 }
 int main(void){
     int T,n,m;
     scanf("%d",&T);
     for(int i=;i<=T;++i){
       /*if(i==10)while(1);
         WA when i==10*/
         init();
         scanf("%d%d",&n,&m);
         for(int j=;j<n;++j){
             int x,y;
             scanf("%d%d",&x,&y);x++,y++;
             e[x].push_back(y);
             e[y].push_back(x);
         }
         for(int j=;j<=n;++j)
             scanf("%I64d",&val[j]);
         dfs(,val[]);
         build(,,n);
         printf("Case #%d:\n",i);
         while(m--){
             int type;
             scanf("%d",&type);
             if(type==){
                 int x,v;
                 scanf("%d%d",&x,&v);x++;
                 LL diff=(LL)v-val[x];
                 val[x]=(LL)v;
                 add(,,n,L[x],R[x],diff);
             }else if(type==){
                 int x;
                 scanf("%d",&x);x++;
                 LL temp=query(,,n,L[x],R[x]);
                 printf("%I64d\n",temp);
             }
         }
     }
     return ;
 }