测试样例：
Input:
6
1 3 5 7 9 11
Output:
35
46
Code：
#pragma GCC optimize(2)
#include<cstdio>
typedef long long ll;
using namespace std;
const int maxn = 10000;
int tree[4*maxn];
int arr[maxn];
int n;
void read_array(void) {
scanf("%d", &n);
for (int i=0;i<n;i++) {
scanf("%d", &arr[i]);
}
}
void build_tree(int node, int left, int right) {
//tree[node] = arr[left] + arr[left+1] + ... + arr[right]
if (left == right) {
tree[node] = arr[left];
} else {
int mid = (left + right) / 2;
int left_node = 2 * node + 1;
int right_node = 2 * node + 2;
build_tree(left_node, left, mid);
build_tree(right_node, mid+1, right);
tree[node] = tree[left_node] + tree[right_node];
}
}
void update_tree(int node, int left, int right, int idx, int val) {
//make arr[idx] = val, then update tree[]
if (left == right) {
tree[node] = val;
arr[idx] = val;
return;
} else if (!(idx >= left && idx <= right)) {
return;
} else {
int mid = (left + right) / 2;
int left_node = 2 * node + 1;
int right_node = 2 * node + 2;
if (idx >= left && idx <= mid)//update left tree
update_tree(left_node, left, mid, idx, val);
else//update right tree
update_tree(right_node, mid+1, right, idx, val);
tree[node] = tree[left_node] + tree[right_node];
}
}
int query_tree(int node, int left, int right, int L, int R) {
//return arr[L] + arr[L+1] + ... + arr[R]
if (R < left || L > right) {
return 0;
} else if (L <= left && right <= R) {
return tree[node];
} else {
int mid = (left + right) / 2;
int left_node = 2 * node + 1;
int right_node = 2 * node + 2;
tree[node] = query_tree(left_node, left, mid, L, R) + query_tree(right_node, mid+1, right, L, R);
return tree[node];
}
}
int main()
{
read_array();
build_tree(0, 0, n-1);
int ans = query_tree(0, 0, n-1, 1, 5);
printf("%d\n", ans);
update_tree(0, 0, n-1, 4, 20);
ans = query_tree(0, 0, n-1, 1, 5);
printf("%d\n", ans);
return 0;
}