POJ 3321-Apple Tree-树状数组+dfs序

Posted 2020-06-23 Helica

计算一个树的子树节点权值和，节点权值可以单个修改。

利用dfs序把一颗树投影到数组里，维护dfs序和子节点个数，然后用树状数组即可。

  1 #include <cstdio>
  2 #include <algorithm>
  3 #include <cstring>
  4 
  5 using namespace std;
  6 
  7 const int maxn = 1e5+10;
  8 int N,M,c[maxn],chdnum[maxn];
  9 int id_dfs[maxn],cnt_dfs;
 10 bool vis[maxn];
 11 
 12 struct Edge{
 13     int to,next;
 14 
 15 }edge[4*maxn];
 16 int head[maxn],tol;
 17 
 18 int add_edge(int u,int v)
 19 {
 20     edge[tol].to = u;
 21     edge[tol].next = head[v];
 22     head[v] = tol++;
 23 
 24     edge[tol].to = v;
 25     edge[tol].next = head[u];
 26     head[u] = tol++;
 27 }
 28 
 29 int dfs(int u)
 30 {
 31     int chd = 1;
 32     vis[u] = true;
 33     if(id_dfs[u] == -1) id_dfs[u] = cnt_dfs++;
 34 
 35     for(int i = head[u];~i;i = edge[i].next) if(!vis[edge[i].to])
 36     {
 37         int v = edge[i].to;
 38         chd += dfs(v);
 39     }
 40     return chdnum[u] = chd;
 41 }
 42 
 43 int lowbit(int x)
 44 {
 45     return x & (-x);
 46 }
 47 
 48 void update(int x,int a)
 49 {
 50     while( x <= N)
 51     {
 52         c[x] += a;
 53         x += lowbit(x);
 54     }
 55 }
 56 
 57 int getsum(int x)
 58 {
 59     int res = 0;
 60     while(x > 0)
 61     {
 62         res += c[x];
 63         x -= lowbit(x);
 64     }
 65     return res;
 66 }
 67 
 68 int query(int l,int r)
 69 {
 70     return getsum(r) - getsum(l-1);
 71 }
 72 
 73 int main()
 74 {
 75     while(~scanf("%d",&N))
 76     {
 77         memset(head,-1,sizeof head);
 78         memset(c,0,sizeof c);
 79         memset(id_dfs,-1,sizeof id_dfs);
 80         memset(vis,false,sizeof vis);
 81         cnt_dfs = 1;
 82         tol = 0;
 83 
 84         for(int i=0,u,v;i<N-1;i++)
 85         {
 86             scanf("%d%d",&u,&v);
 87             add_edge(u,v);
 88         }
 89 
 90         dfs(1);
 91 
 92         for(int i=1;i<=N;i++)
 93         {
 94             //printf("i: dfs:%d\n",i,id_dfs[i]);
 95             update(id_dfs[i],1);
 96         }
 97         scanf("%d",&M);
 98 
 99         char op[5];
100         int x;
101         for(int i=0;i<M;i++)
102         {
103             scanf("%s%d",op,&x);
104             //printf("sum:%d chnum:%d id:%d\n",query(id_dfs[x],id_dfs[x]),chdnum[x],id_dfs[x]);
105             if(op[0] == ‘Q‘)
106             {
107                 printf("%d\n",getsum(id_dfs[x]+chdnum[x]-1) - getsum(id_dfs[x]-1) );
108             }
109             else
110             {
111                 if(query(id_dfs[x],id_dfs[x])) update(id_dfs[x],-1);
112                 else         update(id_dfs[x],1);
113             }
114         }
115     }
116 }