BZOJ 1036：树的统计Count（树链剖分）

http://www.lydsy.com/JudgeOnline/problem.php?id=1036

题意：中文题意。

思路：也是普通的树链剖分。唯一注意的点是在change函数中

     while(top[u] != top[v]) {
         if(dep[top[u]] < dep[top[v]]) swap(u, v);
         if(type == ) ans = max(ans, query(, , tim, tid[top[u]], tid[u], type));
         else ans += query(, , tim, tid[top[u]], tid[u], type);
         u = fa[top[u]];
     }

这里的dep比较的是节点的top节点的深度，而不是直接比较节点的深度。因为这里WA了好久。只能说还未完全理解透细节。

 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <cstring>
 #include <string>
 #include <cmath>
 #include <queue>
 #include <vector>
 using namespace std;
 #define N 30010
 #define INF 10000000000
 #define lson rt<<1, l, m
 #define rson rt<<1|1, m + 1, r

 struct node
 {
     int v, nxt, w;
 }edge[N*];
 int top[N], tid[N], fa[N], son[N], siz[N], dep[N], rak[N], w[N], tim;
 int head[N], tot;
 struct T
 {
     long long sum;
     long long ma;
 }tree[N<<];

 void init()
 {
     memset(head, -, sizeof(head));
     memset(son, -, sizeof(son));
     tot = tim = ;
 }

 void add(int u, int v)
 {
     edge[tot].v = v; edge[tot].nxt = head[u]; head[u] = tot++;
 }

 void dfs1(int u, int f, int d)
 {
     siz[u] = ;
     dep[u] = d;
     fa[u] = f;
     for(int i = head[u]; ~i; i = edge[i].nxt) {
         int v = edge[i].v;
         if(v == f) continue;
         dfs1(v, u, d + );
         siz[u] += siz[v];
         if(son[u] == - || siz[son[u]] < siz[v]) son[u] = v;
     }
 }

 void dfs2(int u, int tp)
 {
     top[u] = tp;
     tid[u] = ++tim;
     rak[tim] = u;
     if(son[u] == -) return ;
     dfs2(son[u], tp);
     for(int i = head[u]; ~i; i = edge[i].nxt) {
         int v = edge[i].v;
         if(v != fa[u] && v != son[u]) dfs2(v, v);
     }
 }

 void pushup(int rt)
 {
     tree[rt].sum = tree[rt<<].sum + tree[rt<<|].sum;
     tree[rt].ma = max(tree[rt<<].ma, tree[rt<<|].ma);
 }

 void build(int rt, int l, int r)
 {
     tree[rt].sum = ;
     tree[rt].ma = ;
     if(l == r) {
         tree[rt].sum = w[rak[l]];
         tree[rt].ma = w[rak[l]];
         return ;
     }
     int m = (l + r) >> ;
     build(lson); build(rson);
     pushup(rt);
 }

 void update(int rt, int l, int r, int id, int val)
 {
     if(l == r && l == id) {
         tree[rt].sum = val;
         tree[rt].ma = val;
         return ;
     }
     int m = (l + r) >> ;
     if(id <= m) update(lson, id, val);
     else update(rson, id, val);
     pushup(rt);
 }

 long long query(int rt, int l, int r, int L, int R, int type)
 {
     long long ans = ;
     if(type == ) ans = -INF;
     if(L <= l && r <= R) {
         if(type == ) ans = max(ans, tree[rt].ma);
         else ans += tree[rt].sum;
         return ans;
     }
     int m = (l + r) >> ;
     if(L <= m) {
         if(type == ) ans = max(ans, query(lson, L, R, type));
         else ans += query(lson, L, R, type);
     }
     if(m < R) {
         if(type == ) ans = max(ans, query(rson, L, R, type));
         else ans += query(rson, L, R, type);
     }
     return ans;
 }

 long long change(int u, int v, int type)
 {
     long long ans = ;
     if(type == ) ans = -INF;
     while(top[u] != top[v]) {
         if(dep[top[u]] < dep[top[v]]) swap(u, v);
         if(type == ) ans = max(ans, query(, , tim, tid[top[u]], tid[u], type));
         else ans += query(, , tim, tid[top[u]], tid[u], type);
         u = fa[top[u]];
     }
     if(dep[u] > dep[v]) swap(u, v);
     if(type == ) ans = max(ans, query(, , tim, tid[u], tid[v], type));
     else ans += query(, , tim, tid[u], tid[v], type);
     return ans;
 }

 int main()
 {
     int n, q;
     scanf("%d", &n);
     init();
     for(int i = ; i < n; i++) {
         int u, v;
         scanf("%d%d", &u, &v);
         add(u, v); add(v, u);
     }
     for(int i = ; i <= n; i++) scanf("%d", &w[i]);
     dfs1(, , );
     dfs2(, );
     build(, , tim);
     // for(int i = 1; i <= n; i++) printf("tid[%d] : %d\n", i, tid[i]);
     scanf("%d", &q);
     while(q--) {
         char s[];
         int a, b;
         scanf("%s%d%d", s, &a, &b);
         if(s[] == 'C') {
             update(, , tim, tid[a], b);
         } else {
             int type = ;
             if(s[] == 'S') type = ;
             printf("%lld\n", change(a, b, type));
         }
     }
     return ;
 }