树状数组

 1 #include <iostream>
 2 #include <stdio.h>
 3 #include <string.h>
 4 
 5 using namespace std;
 6 #define MAXN 1000
 7 
 8 int n;
 9 int A[MAXN];
10 int C[MAXN];
11 
12 int lowbit(int x)
13 {
14     return x&(-x);
15 }
16 
17 void new_tree(int n)    // 建树 大概 n*log(n)
18 {
19     memset(C,0,sizeof(C));
20     for (int i=1;i<=n;i++)
21     {
22         C[i]+=A[i];
23         for (int j=i+lowbit(i);j<=n;j+=lowbit(j))   //性质2
24             C[j]+=A[i];
25     }
26 }
27 
28 void update(int x,int add) //A[x]增减
29 {
30     A[x]+=add;
31     while (x<=n)
32     {
33         C[x]+=add;
34         x+=lowbit(x);
35     }
36 }
37 
38 int getsum(int x)//[1--x]的和
39 {
40     int sum=0;
41     while(x>0)
42     {
43         sum+=C[x];
44         x -= lowbit(x); //性质1
45     }
46     return sum;
47 }
48 
49 int main()
50 {
51     scanf("%d",&n);
52     for (int i=1;i<=n;i++)
53         scanf("%d",&A[i]);
54     new_tree(n);
55 
56     int l,r;
57     scanf("%d %d",&l,&r);
58     printf("%d\n",getsum(r)-getsum(l-1)); //l--r 的和
59 
60     return 0;
61 }