SPOJ - QTREE5 Query on a tree V 边分治

题目传送门

题意：给你一棵树， 然后树上的点都有颜色，且原来为黑，现在有2个操作，1 改变某个点的颜色， 2 询问树上的白点到u点的最短距离是多少。

题解：

这里用的还是边分治的方法。

把所有东西都抠出来， 然后每次询问的时候都访问每幅分割图的另外一侧。

代码：

 #include<bits/stdc++.h>
 using namespace std;
 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 #define LL long long
 #define ULL unsigned LL
 #define fi first
 #define se second
 #define pb push_back
 #define lson l,m,rt<<1
 #define rson m+1,r,rt<<1|1
 #define lch(x) tr[x].son[0]
 #define rch(x) tr[x].son[1]
 #define max3(a,b,c) max(a,max(b,c))
 #define min3(a,b,c) min(a,min(b,c))
 typedef pair<int,int> pll;
 const int inf = 0x3f3f3f3f;
 const LL INF = 0x3f3f3f3f3f3f3f3f;
 const LL mod =  (int)1e9+;
 const int N = 2e5 + ;
 struct Node{
     int head[N], to[N<<], nt[N<<], ct[N<<];
     int tot;
     void init(){
         memset(head, -, sizeof(head));
         tot = ;
     }
     void add(int u, int v, int cost){
         ct[tot] = cost;
         to[tot] = v;
         nt[tot] = head[u];
         head[u] = tot++;
     }
 }e[];
 int n, m, white[N], cut[N<<];
 void rebuild(int o, int u){
     int ff = ;
     for(int i = e[].head[u]; ~i; i = e[].nt[i]){
         int v = e[].to[i];
         if(o == v) continue;
         if(!ff){
             e[].add(u, v, );
             e[].add(v, u, );
             ff = u;
         }
         else {
             ++n;
             e[].add(ff, n, ); e[].add(n, ff, );
             e[].add(n, v, ); e[].add(v, n, );
             ff = n;
         }
         rebuild(u, v);
     }
 }
 int sz[N], minval, id;
 void get_edge(int o, int u, int num){
     sz[u] = ;
     for(int i = e[].head[u]; ~i; i = e[].nt[i]){
         int v = e[].to[i];
         if(v == o || cut[i>>]) continue;
         get_edge(u, v, num);
         sz[u] += sz[v];
         int tmp = max(sz[v], num - sz[v]);
         if(tmp < minval){
             minval = tmp;
             id = i;
         }
     }
 }
 int k = , op;
 vector<pll> vc[N];
 priority_queue<pll, vector<pll>, greater<pll> > pq[N<<][];
 int wedge[N<<];
 int mm;
 void dfs2(int o, int u, int w){
     vc[u].pb(pll(k*op, w));
     sz[u] = ;
     for(int i = e[].head[u]; ~i; i = e[].nt[i]){
         int v = e[].to[i];
         if(v == o || cut[i>>]) continue;
         dfs2(u, v, w + e[].ct[i]);
         sz[u] += sz[v];
     }
 }
 void solve(int u, int num){
     if(num <= ) return ;
     minval = inf;
     get_edge(, u, num);
     int nid = id;
     cut[nid>>] = ;
     ++k;
     op = ;
     dfs2(, e[].to[nid], );
     op = -;
     dfs2(, e[].to[nid^], );
     wedge[k] = e[].ct[nid];
     solve(e[].to[nid], sz[e[].to[nid]]);
     solve(e[].to[nid^], sz[e[].to[nid^]]);
 }
 void Update(int k){
     while(!pq[k][].empty() && !white[pq[k][].top().se]) pq[k][].pop();
     while(!pq[k][].empty() && !white[pq[k][].top().se]) pq[k][].pop();
 }
 void setwhite(int u){
     for(int i = ; i < vc[u].size(); i++){
         int k = vc[u][i].fi, w = vc[u][i].se;
         if(k < ) pq[-k][].push(pll(w,u));
         else pq[k][].push(pll(w,u));
         Update(abs(k));
     }
 }
 void setblack(int u){
     for(int i = ; i < vc[u].size(); i++){
         int k = vc[u][i].fi;
         Update(abs(k));
     }
 }
 int Find(int u){
     int ret = inf;
     for(int i = ; i < vc[u].size(); i++){
         int k = vc[u][i].fi, w = vc[u][i].se;
         if(k <  && !pq[-k][].empty())
                 ret = min(ret, w+wedge[-k]+pq[-k][].top().fi);
         if(k >  && !pq[k][].empty())
             ret = min(ret, w+wedge[k]+pq[k][].top().fi);
     }
     return ret;
 }
 int main(){
     e[].init(); e[].init();
     scanf("%d", &n);
     int u, v;
     for(int i = ; i < n; i++){
         scanf("%d%d", &u, &v);
         e[].add(u, v, ); e[].add(v, u, );
     }
     memset(white, , sizeof(white));
     rebuild(, );
     solve(, n);
     int num = , op;
     scanf("%d", &m);
     while(m--){
         scanf("%d%d", &op, &v);
         if(op == ){
             white[v] ^= ;
             if(white[v]){
                 setwhite(v);
                 num++;
             }
             else {
                 setblack(v);
                 num--;
             }
         }
         else {
             if(num == ) puts("-1");
             else if(white[v]) puts("");
             else {
                 printf("%d\n", Find(v));
             }
         }
     }
     return ;
 }