POJ 2763 Housewife Wind（树链剖分+树状数组）

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N=200010; 
int tot,x,d[N],num[N],ed=0,u,w,n,m,i,v[N],vis[N],f[N],g[N];
int nxt[N],size[N],son[N],st[N],en[N],dfn,top[N],t;char ch;
void add_edge(int x,int y){v[++ed]=y;nxt[ed]=g[x];g[x]=ed;}
void init(){ 
    memset(g,dfn=ed=0,sizeof(g));
    memset(v,0,sizeof(v));
    memset(nxt,0,sizeof(nxt));
    memset(son,-1,sizeof(son));
}
void dfs(int x){
    size[x]=1;
    for(int i=g[x];i;i=nxt[i])if(v[i]!=f[x]){
        f[v[i]]=x,d[v[i]]=d[x]+1;
        dfs(v[i]),size[x]+=size[v[i]];
        if(size[v[i]]>size[son[x]])son[x]=v[i];
    }
}
void dfs2(int x,int y){
    if(x==-1)return;
    st[x]=++dfn;top[x]=y;
    if(son[x])dfs2(son[x],y);
    for(int i=g[x];i;i=nxt[i])if(v[i]!=son[x]&&v[i]!=f[x])dfs2(v[i],v[i]);
    en[x]=dfn;
}
int c[N];
void add(int x,int val){while(x<=dfn)c[x]+=val,x+=x&-x;}
int query(int x){int s=0;while(x)s+=c[x],x-=x&-x;return s;}
int chain(int x,int y){
    int res=0;
    for(;top[x]!=top[y];x=f[top[x]]){
        if(d[top[x]]<d[top[y]]){int z=x;x=y;y=z;}
        res=res+query(st[x])-query(st[top[x]]-1);
    }if(d[x]<d[y]){int z=x;x=y;y=z;}
    //注意边权转为子节点点权时，链操作不操作deep最浅的点,左端点为开节点
    res=res+query(st[x])-query(st[y]);
    return res; 
}
int e[N][3],q,s;
int main(){
    while(~scanf("%d%d%d",&n,&q,&s)){
        init();
        memset(c,0,sizeof(c));
        for(int i=1;i<n;i++){
            scanf("%d%d%d",&e[i][0],&e[i][1],&e[i][2]);
            add_edge(e[i][0],e[i][1]);
            add_edge(e[i][1],e[i][0]);
        }dfs(1);dfs2(1,1);
        for(int i=1;i<n;i++){
            if(d[e[i][0]]>d[e[i][1]])swap(e[i][0],e[i][1]);
            add(st[e[i][1]],e[i][2]);
        }int op,x,y;
        while(q--){
            scanf("%d",&op);
            if(op==0){
                scanf("%d",&x);
                printf("%d\n",chain(x,s));
                s=x;
            }else{
                scanf("%d%d",&x,&y);
                add(st[e[x][1]],y-e[x][2]);
                e[x][2]=y;
            }
        }
    }return 0;
}