Binary Indexed Tree实现 国内称作 树状数组

国内资料：http://baike.baidu.com/view/1420784.htm

国外资料：http://community.topcoder.com/tc?module=Static&d1=tutorials&d2=binaryIndexedTrees

重点：

储存策略，更新策略，查找策略， x & (-x)的证明

数组从1开始

自己实现的代码如下：

#include <iostream>int const N = 1000;int tree[N];void updateBIT(int* a, int idx, int len){int val = a[idx];while(idx <= len){tree[idx] += val;idx += (idx & (-idx));}};void buildBIT(int* a, int len){memset(tree, 0, len * sizeof(int));for(int i = 1; i <= len; i++){updateBIT(a, i, len);}};int getSum(int idx){int sum = 0;while(idx > 0){sum += tree[idx];idx -= (idx & (-idx));}return sum;};int main(){int a[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20};buildBIT(a, 20);for(int i = 1; i <= 20; i++){std::cout << "Sum[" << i << "] = " << getSum(i) << std::endl;}return 0;}