SPOJ375 Query on a tree(树链剖分)

传送门

题意

给出一棵树，每条边都有权值，有两种操作：

• 把第p条边的权值改为x
• 询问x，y路径上的权值最大的边

code

 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1

 using namespace std;

 const int N = ;
 struct Edge {
     int to,nxt,w;
 }e[];
 int head[N],tot,tn,n;
 int deth[N],son[N],fa[N],siz[N],bel[N],pos[N];
 int mx[N<<],a[N],b[N],c[N],data[N];

 void init() {
     tot = tn = ;
     memset(head,,sizeof(head));
     memset(son,,sizeof(son));
 }
 inline void add_edge(int u,int v,int w) {
     e[++tot].to = v,e[tot].w = w,e[tot].nxt = head[u],head[u] = tot;
 }
 void dfs1(int u,int pa) {
     siz[u] = ;
     for (int i=head[u]; i; i=e[i].nxt) {
         int v = e[i].to;
         if (v==pa) continue;
         fa[v] = u;
         deth[v] = deth[u] + ;
         dfs1(v,u);
         siz[u] += siz[v];
         if (son[u]== || siz[v] > siz[son[u]]) son[u] = v;
     }
 }
 void dfs2(int u,int top) {
     pos[u] = ++tn;
     bel[u] = top;
     if (!son[u]) return ;
     dfs2(son[u],top);
     for (int i=head[u]; i; i=e[i].nxt) {
         int v = e[i].to;
         if (v != fa[u] && v != son[u]) dfs2(v,v);
     }
 }
 void pushup(int rt) {
     mx[rt] = max(mx[rt<<],mx[rt<<|]);
 }
 void build(int l,int r,int rt) {
     if (l==r) {
         mx[rt] = data[l];return ;
     }
     int m = (l + r) >> ;
     build(lson);
     build(rson);
     pushup(rt);
 }
 void update(int l,int r,int rt,int p,int x) {
     if (l==r) {
         mx[rt] = x;return ;
     }
     int m = (l + r) >> ;
     if (p <= m) update(lson,p,x);
     else update(rson,p,x);
     pushup(rt);
 }
 int query(int l,int r,int rt,int L,int R) {
     if (L <= l && r <= R) {
         return mx[rt];
     }
     int m = (l + r) >> ;
     int ret = -1e9;
     if (L <= m) ret = max(ret,query(lson,L,R));
     if (R > m)  ret = max(ret,query(rson,L,R));
     return ret;
 }
 void Change(int p,int x) {
     if (deth[a[p]] > deth[b[p]]) update(,n,,pos[a[p]],x);
     else update(,n,,pos[b[p]],x);
 }
 int Ask(int x,int y) {
     int ans = -1e9;
     while (bel[x] != bel[y]) {
         if (deth[bel[x]] < deth[bel[y]]) swap(x,y);
         ans = max(ans,query(,n,,pos[bel[x]],pos[x]));
         x = fa[bel[x]];
     }
     if (deth[x] > deth[y]) swap(x,y);
     if (x != y) ans = max(ans,query(,n,,pos[x]+,pos[y]));
     return ans;
 }
 int main() {
     char opt[];
     int T;scanf("%d",&T);
     while (T--) {
         init();
         scanf("%d",&n);
         for (int i=; i<n; ++i) {
             scanf("%d%d%d",&a[i],&b[i],&c[i]);
             add_edge(a[i],b[i],c[i]);
             add_edge(b[i],a[i],c[i]);
         }
         deth[] = ;
         dfs1(,);
         dfs2(,);
         for (int i=; i<n; ++i) {
             if (deth[a[i]] > deth[b[i]]) data[pos[a[i]]] = c[i]; // 一定是pos
             else data[pos[b[i]]] = c[i];
         }
         build(,n,);
         scanf("%s",opt);
         while (opt[]!='D') {
             int x,y;
             scanf("%d%d",&x,&y);
             if (opt[]=='Q') printf("%d\n",Ask(x,y));
             else Change(x,y);
             scanf("%s",opt);
         }
     }
     return ;
 }