hdu 4046 Panda（树状数组）

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <algorithm>
 4 using namespace std;
 5 
 6 const int N = 50007;
 7 
 8 int tree[N], n;
 9 char str[N];
10 
11 int lowbit(int x)
12 {
13     return (x & -x);
14 }
15 
16 void update(int pos, int val)
17 {
18     while (pos <= n)
19     {
20         tree[pos] += val;
21         pos += lowbit(pos);
22     }
23 }
24 
25 int find(int pos)
26 {
27     int sum = 0;
28     while (pos > 0)
29     {
30         sum += tree[pos];
31         pos -= lowbit(pos);
32     }
33     return sum;
34 }
35 
36 int main()
37 {
38     int t, m, cas;
39     while (scanf("%d", &t) != EOF)
40     {
41         cas = 0;
42         while (t--)
43         {
44             memset(tree, 0, sizeof(tree));
45             printf("Case %d:\n", ++cas);
46             scanf("%d%d", &n, &m);
47             getchar();
48             scanf("%s", str + 1);
49             for (int i = 3; i <= n; i++)
50             {
51                 if (str[i] == ‘w‘ && str[i-1] == ‘b‘ && str[i-2] == ‘w‘)
52                     update(i, 1);
53             }
54             int op;
55             for (int i = 0; i < m; i++)
56             {
57                 scanf("%d", &op);
58                 if (op == 0)
59                 {
60                     int a, b;
61                     scanf("%d%d", &a, &b);
62                     a++, b++;
63                     if (b - a < 2)
64                         printf("0\n");
65                     else
66                         printf("%d\n", find(b) - find(a + 1));
67                 }
68                 else
69                 {
70                     int a;
71                     char c;
72                     scanf("%d %c", &a, &c);
73                     a++;
74                     if (str[a] == c)
75                         continue;
76                     if (a >= 3 && str[a] == ‘w‘ && str[a-1] == ‘b‘ && str[a-2] == ‘w‘)
77                         update(a, -1);
78                     if (a > 1 && a <= n - 1 && str[a-1] == ‘w‘ && str[a] == ‘b‘ && str[a+1] == ‘w‘)
79                         update(a + 1, -1);
80                     if (a <= n - 2 && str[a] == ‘w‘ && str[a+1] == ‘b‘ && str[a+2] == ‘w‘)
81                         update(a + 2, -1);
82                     str[a] = c;
83                     if (a >= 3 && str[a] == ‘w‘ && str[a-1] == ‘b‘ && str[a-2] == ‘w‘)
84                         update(a, 1);
85                     if (a > 1 && a <= n - 1 && str[a-1] == ‘w‘ && str[a] == ‘b‘ && str[a+1] == ‘w‘)
86                         update(a + 1, 1);
87                     if (a <= n - 2 && str[a] == ‘w‘ && str[a+1] == ‘b‘ && str[a+2] == ‘w‘)
88                         update(a + 2, 1);
89                 }
90             }
91         }
92     }
93 }