codechef Tree and Queries Solved

题目链接：

https://www.codechef.com/problems/IITK1P10

 大概是：修改点值，求子树节点为0有多少个，

DFS序后,BIT 询问，修改

 1 #include<bits/stdc++.h>
 2 
 3 using namespace std;
 4 typedef long long ll;
 5 
 6 #define N 223456
 7 ll val[N];
 8 int l[N],r[N];
 9 int t=1;
10 int f[N];
11 int lowbit(int x)
12 {
13     return x&-x;
14 }
15 void update(int x,int v)
16 {
17     while (x<N)
18     {
19         f[x]+=v;
20         x+=lowbit(x);
21     }
22 }
23 ll query(int x)
24 {
25     ll s=0;
26     while (x)
27     {
28         s+=f[x];
29         x-=lowbit(x);
30     }
31     return s;
32 }
33 vector<int>mp[N];
34 void dfs(int u,int pre)
35 {
36     l[u]=t++;
37     for (int i=0;i<mp[u].size();i++)
38     {
39         int v=mp[u][i];
40         if (v==pre) continue;
41         dfs(v,u);
42     }
43     r[u]=t-1;
44 }
45 
46 
47 int main()
48 {
49     int n,Q;
50     scanf("%d%d",&n,&Q);
51     for (int i=1;i<n;i++)
52     {
53         int x,y;
54         scanf("%d%d",&x,&y);
55         mp[x].push_back(y);
56         mp[y].push_back(x);
57     }
58     dfs(1,0);
59     for (int i=1;i<=n;i++)
60     {
61         scanf("%d",&val[i]);
62         if (val[i]==0) update(l[i],1);
63     }
64     while (Q--)
65     {
66         char s[4];
67         scanf("%s",s);
68         if (s[0]=='U')
69         {
70             int u,v;
71             scanf("%d%d",&u,&v);
72             if (val[u]==0) update(l[u],-1);
73             val[u]+=v;
74             if (val[u]==0) update(l[u],1);
75         }else
76         {
77             int x;
78             scanf("%d",&x);
79             int ans=query(r[x])-query(l[x]-1);
80             printf("%d\n",ans);
81         }
82     }
83     return 0;
84 }