POJ 3321-Apple Tree-樹狀數組+dfs序

標籤：

計算一個樹的子樹節點權值和，節點權值可以單個修改。

利用dfs序把一顆樹投影到數組裡，維護dfs序和子節點個數，然後用樹狀數組即可。

  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             else110             {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 }

 

POJ 3321-Apple Tree-樹狀數組+dfs序