【SPOJ QTREE】树链剖分模板

用线段树求解，这里注意因为求的是路径最大值，注意一下细节。

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int MAXN = 10010;
#define lson (pos<<1)
#define rson (pos<<1|1)
const int INF = (1 << 30);
int n;
//--------------------------------------------------
struct Edge{
    int to,next;
}edge[MAXN * 2];
int head[MAXN],tot;
int top[MAXN];
int fa[MAXN];
int deep[MAXN];
int num[MAXN];
int p[MAXN];
int fp[MAXN];
int son[MAXN];
int pos;
void init(){
    tot = 0;
    memset(head,-1,sizeof(head));
    pos = 1;
    memset(son,-1,sizeof(son));
}
void addedge(int u,int v){
    edge[tot].to = v;
    edge[tot].next = head[u];
    head[u] = tot ++;
}
void dfs1(int u,int pre,int d){
    deep[u] = d;
    fa[u] = pre;
    num[u] = 1;
    for(int i = head[u]; i != -1; i = edge[i].next){
        int v = edge[i].to;
        if(v != pre){
            dfs1(v,u,d + 1);
            num[u] += num[v];
            if(son[u] == -1 || num[v] > num[son[u]])
                son[u] = v; //找重儿子
        }
    }
}
void getpos(int u,int sp){
    top[u] = sp;
    p[u] = pos++;
    //printf("%d %d\n",u,p[u]);
    fp[p[u]] = u;
    if(son[u] == -1) return;
    getpos(son[u],sp);
    for(int i = head[u]; i != -1; i = edge[i].next){
        int v = edge[i].to;
        if(v != son[u] && v!= fa[u])
            getpos(v,v);
    }
}
//----------------------------------------------
int maxv[MAXN << 2];            //该一条边
void build(){
    memset(maxv,0,sizeof(maxv));
}
void pushup(int pos){
    maxv[pos] = max(maxv[lson],maxv[rson]);
}
void update(int l,int r,int to,int value,int pos){
    if(l == r){
        maxv[pos] = value;
        return;
    }
    int mid = (l + r) >> 1;
    if(to <= mid)
        update(l,mid,to,value,lson);
    else
        update(mid + 1,r,to,value,rson);
    pushup(pos);
}
int query(int l,int r,int L,int R,int pos){
    if(L <= l && r <= R)
        return maxv[pos];
    int mid = (l + r) >> 1;
    int ret = - INF;
    if(L <= mid)
        ret = max(ret,query(l,mid,L,R,lson));
    if(R  > mid)
        ret = max(ret,query(mid + 1,r,L,R,rson));
    return ret;
}
//-------------------------------------------------------
int find(int u,int v){
    int f1 = top[u],f2 = top[v];
    int tmp = 0;
    while(f1 != f2){
        if(deep[f1] < deep[f2]){
            swap(f1,f2);
            swap(u,v);
        }
        tmp = max(tmp,query(1,pos,p[f1],p[u],1));
        u = fa[f1];
        f1 = top[u];
    }
    if(u == v) return tmp;
    if(deep[u] > deep[v]) swap(u,v);
    return max(tmp,query(1,pos,p[son[u]],p[v],1));
}
//----------------------------------------------------------
struct E{
    int from,to,value;
}e[MAXN];
int main(){
    int T;
    int u,v;
    scanf("%d",&T);
    while(T--){
        scanf("%d",&n);
        init();
        for(int i = 0; i < n - 1; i++){
            scanf("%d%d%d",&e[i].from,&e[i].to,&e[i].value);
            addedge(e[i].from,e[i].to);
            addedge(e[i].to,e[i].from);
        }
        dfs1(1,0,0);
        getpos(1,1);
        build();
        for(int i = 0; i < n - 1; i++){
            if(deep[e[i].from] > deep[e[i].to])
                swap(e[i].from,e[i].to);            //这里是更新一条线段，不是一个点
            update(1,pos,p[e[i].to],e[i].value,1);
        }
        char op[10];
        while(scanf("%s",op) != EOF){
            if(op[0] == 'D') break;
            scanf("%d%d",&u,&v);
            if(op[0] == 'Q'){
                printf("%d\n",find(u,v));
            }
            else{
                update(1,pos,p[e[u - 1].to],v,1);
            }
        }
        if(T) puts("");
    }
    return 0;
}