HDU 4046 Panda

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 50010;
 4 struct node{
 5     int lt,rt,sum;
 6 }tree[maxn<<2];
 7 int num[maxn];
 8 void build(int L,int R,int v){
 9     tree[v].lt = L;
10     tree[v].rt = R;
11     if(L == R){
12         tree[v].sum = num[L];
13         return;
14     }
15     int mid = (L + R)>>1;
16     build(L,mid,v<<1);
17     build(mid+1,R,v<<1|1);
18     tree[v].sum = tree[v<<1].sum + tree[v<<1|1].sum;
19 }
20 void update(int id,int val,int v){
21     if(tree[v].lt == tree[v].rt){
22         tree[v].sum = val;
23         return;
24     }
25     int mid = (tree[v].lt + tree[v].rt)>>1;
26     if(id <= mid) update(id,val,v<<1);
27     if(id > mid) update(id,val,v<<1|1);
28     tree[v].sum = tree[v<<1].sum + tree[v<<1|1].sum;
29 }
30 int query(int lt,int rt,int v){
31     if(lt <= tree[v].lt && rt >= tree[v].rt) return tree[v].sum;
32     int mid = (tree[v].lt + tree[v].rt)>>1,ans = 0;
33     if(lt <= mid) ans += query(lt,rt,v<<1);
34     if(rt > mid) ans += query(lt,rt,v<<1|1);
35     return ans;
36 }
37 char str[maxn],tmp[20];
38 int main(){
39     int T,n,m,op,a,b,cs = 1;
40     scanf("%d",&T);
41     while(T--){
42         scanf("%d %d",&n,&m);
43         scanf("%s",str);
44         printf("Case %d:\n",cs++);
45         memset(num,0,sizeof num);
46         for(int i = 2; i < n; ++i)
47             if(str[i-2] == ‘w‘ && str[i-1] == ‘b‘ && str[i] == ‘w‘) num[i] = 1;
48         build(0,n-1,1);
49         while(m--){
50             scanf("%d %d",&op,&a);
51             if(op){
52                 scanf("%s",tmp);
53                 if(str[a] == tmp[0]) continue;
54                 if(a >= 2 && str[a-2] == ‘w‘ && str[a-1] ==‘b‘)
55                     update(a,str[a] == ‘w‘?0:1,1);
56                 if(a >= 1 && a + 1 < n && str[a-1] == ‘w‘ && str[a+1] == ‘w‘)
57                     update(a+1,str[a] == ‘b‘?0:1,1);
58                 if(a + 2 < n && str[a+1] == ‘b‘ && str[a+2] == ‘w‘)
59                     update(a+2,str[a] == ‘w‘?0:1,1);
60                 str[a] = tmp[0];
61             }else{
62                 scanf("%d",&b);
63                 printf("%d\n",b-a<2?0:query(a+2,b,1));
64             }
65         }
66     }
67     return 0;
68 }